Synopses of Oral Papers

IMRT plans by using 6 MV photon beam. For the first and second plans A comparative study of three coplanar IMRT plans for fatty we used 5 fields. The gantry angles were 35°, 100°, 180°, 270° and prostate patients by using pinnacle 3-D treatment planning 325° and 0°, 75°, 135°, 225° and 285° respectively; with couch angle 0°. The third plan had 7 fields for which the gantry angles were 0°, Suvendu Sahoo, AK Rath, NK Painuly, BK Mohanta, H Mod*, 51°, 102°, 153°, 204°, 255° and 306° with couch angle 0°. ICRU 50 S Pattnaik*. Dept. of Medical Physics and *Radiation Oncology, recommendation was followed for the contouring of CTV and other Hemalata Hospitals and Research Center, Bhubaneswar, Orissa, India critical structures. The PTV was generated from CTV having 5 mm 3D­ marigin. The critical structures taken were rectum, bladder and the Introduction: For localized prostate cancer; radiation therapy is an femoral heads. Our study has compared three plans on the basis of effective modality. Prostate is one of the sites that is well suited for dose volume histograms (DVH) of all parameters like PTV and other all IMRT. IMRT planning and treatment delivery show significant potential critical structures. for further improving the therapeutic ratio and reducing toxicity and Results and Discussion: The effect of number of beams in IMRT thereby improving the quality of life. It is the responsibility of the planning for fatty cases is an important decision for a planner. The medical physicist (planner) to obtain an optimal IMRT plan. The purpose mean data of DVH of 5 patients for 3 IMRT plans are given in the of this study is to highlight some important points that need to be Tables. It was seen that, out of the three plans; the third plan was taken care of before embarking upon the IMRT plan. These are: (A) most suitable for patient treatment because the out side PTV maximum the treatment site (B) the facilities available with machine i.e., number dose was much higher in first two plans and comparatively less in the of photon beams, MLC or mMLC and (C) the patient separation third plan. It was seen that in the case of fatty patients the beam path (thickness) from all sides. Of the above three points; first two points length is more in patient body thereby leading to more deposition of are well known to a planner. We want to highlight the third point i.e., dose in the patient body comparative to Planning Target Volume in 5 the patient thickness, which is an important parameter when planning field plans. But in case of 7 fields plan, due to more number of beams IMRT for prostate cancer. Our objective is to show by comparing three the deposition of dose out side PTV was less thereby delivering the co-planner particular IMRT plans; the effect of numbers of beams maximum dose to planning target volume. from various directions on the final dose distribution. Conclusion: This study states that, for fatty prostate patients the 7 Materials and Methods: Our centre is equipped with PINNACLE 3fields IMRT plan is a better optimum plan as compared to a 5 fields D treatment planning system and digital linear accelerator (ELEKTA) IMRT plan. This conclusion will thus be helpful to a planner during a having 40 pairs MLC facility, each MLC width is 1 cm at isocenter. For prostate IMRT planning. our study we took 5 patients of localized prostate cancer, whose AP­ PA separations were 26 to 30 cm and lateral separations were 36 to 40 O-02 cm. For the above comparative study we generated three coplanar Study of dose modeling for IMRT beamlets Sudesh Deshpande, Suresh Chaudhari, V Anand, Sandeep De, Table 1: PTV dose comparison V Kannan. Department of Radiation Oncology, P. D. Hinduja National Hospital and Medical Research Center, Mahim, Mumbai, India PTV PTV min PTV max PTV mean coverage dose dose dose Introduction: Intensity modulated radiation therapy (IMRT) beams (Gy.) (Gy.) (Gy.) are created by using a segmentation algorithm that converts the PLAN-1 (5 FIELDS) 95% 58.16 80.42 74.92 ideal fluence map into deliverable beam segments. This fluence can system


SYNOPSES OF ORAL PAPERS
IMRT plans by using 6 MV photon beam. For the first and second plans A comparative study of three coplanar IMRT plans for fatty we used 5 fields. The gantry angles were 35°, 100°, 180°, 270° and prostate patients by using pinnacle 3-D treatment planning 325° and 0°, 75°, 135°, 225° and 285° respectively; with couch angle 0°. The third plan had 7 fields for which the gantry angles were 0°, Suvendu Sahoo, AK Rath, NK Painuly, BK Mohanta, H Mod*, 51°, 102°, 153°, 204°, 255° and 306° with couch angle 0°. ICRU 50 S Pattnaik*. Dept. of Medical Physics and *Radiation Oncology, recommendation was followed for the contouring of CTV and other Hemalata Hospitals and Research Center, Bhubaneswar, Orissa, India critical structures. The PTV was generated from CTV having 5 mm 3D marigin. The critical structures taken were rectum, bladder and the Introduction: For localized prostate cancer; radiation therapy is an femoral heads. Our study has compared three plans on the basis of effective modality. Prostate is one of the sites that is well suited for dose volume histograms (DVH) of all parameters like PTV and other all IMRT. IMRT planning and treatment delivery show significant potential critical structures. for further improving the therapeutic ratio and reducing toxicity and Results and Discussion: The effect of number of beams in IMRT thereby improving the quality of life. It is the responsibility of the planning for fatty cases is an important decision for a planner. The medical physicist (planner) to obtain an optimal IMRT plan. The purpose mean data of DVH of 5 patients for 3 IMRT plans are given in the of this study is to highlight some important points that need to be Tables. It was seen that, out of the three plans; the third plan was taken care of before embarking upon the IMRT plan. These are: (A) most suitable for patient treatment because the out side PTV maximum the treatment site (B) the facilities available with machine i.e., number dose was much higher in first two plans and comparatively less in the of photon beams, MLC or mMLC and (C) the patient separation third plan. It was seen that in the case of fatty patients the beam path (thickness) from all sides. Of the above three points; first two points length is more in patient body thereby leading to more deposition of are well known to a planner. We want to highlight the third point i.e., dose in the patient body comparative to Planning Target Volume in 5 the patient thickness, which is an important parameter when planning field plans. But in case of 7 fields plan, due to more number of beams IMRT for prostate cancer. Our objective is to show by comparing three the deposition of dose out side PTV was less thereby delivering the co-planner particular IMRT plans; the effect of numbers of beams maximum dose to planning target volume. from various directions on the final dose distribution.
Conclusion: This study states that, for fatty prostate patients the 7 Materials and Methods: Our centre is equipped with PINNACLE 3-fields IMRT plan is a better optimum plan as compared to a 5 fields D treatment planning system and digital linear accelerator (ELEKTA) IMRT plan. This conclusion will thus be helpful to a planner during a having 40 pairs MLC facility, each MLC width is 1 cm at isocenter. For prostate IMRT planning. our study we took 5 patients of localized prostate cancer, whose AP PA separations were 26 to 30 cm and lateral separations were 36 to 40 O-02 cm. For the above comparative study we generated three coplanar Study of dose modeling for IMRT beamlets Sudesh Deshpande, Suresh Chaudhari, V Anand, Sandeep De,   be delivered using step and shoot technique or dynamic sliding window technique. For accurate optimization, dose calculation and segmentation treatment planning system (TPS) need to be accurately modeled. AAPM TG report 53 and TRS 423 described different quality assurance tests for treatment planning system. All commercial treatment planning system passes these tests well within specified limit. Since these tests are designed basically for 3D-CRT most of the test are for square and rectangular fields. Many treatment planning systems require dosimetric data from field size 4*4 to 40*40 cm 2 shaped with secondary collimator. In case of single focus MLC IMRT delivery; secondary jaws are away from MLC leaf end therefore scattering, leakage and dosimetric property will change. It is important for treatment planning systems to compute the dose distributions created by small MLC beamlets and off axis from the center accurately. The purpose of this work is to perform quality assurance tests that simulate different segments of IMRT field. Dose measurements are done within field and outside fields and compared with treatment planning system. was positioned away from beam central axis in 1-cm steps. So that the final seventh field was centered 6 cm away from the central axis. Secondary jaws position were kept at 13.6*20.4 cm 2 , which was a same, as recommended jaw position for IMRT field of 12*20. Percentage depth dose (PDD) was measured for all seven beamlets with 0.01cc chamber and photon diode in RFA 300 (Scanditronix and Wellhofer Germany). All PDD curves were normalized at 1.5 cm. All seven MLC beamlets were used to measure dose profile parallel to direction of beam travel passing through center axis. Dose profile measurement was done at 5 cm using EDR2 film in solid phantom. Film was analyzed with Ominopro software. The LINAC used for this study has single focused MLC of 80 leaves (Varian 2300 CD). Only 6MV-photon beam was used in this study. In eclipse treatment planning system 30*30 images at Omnipro IMRT system created an image proportional to dose. Renormalized the composed image at central axis to 100%. The Adac Pinnacle planning system used for IMRT planning calculates planar dose at a predefined source to plane distance. Planar dose at 5 cm depth for the corresponding field was imported to the software from the planning system. Each field was evaluated by comparing two dimensional reconstructed fluence map from EPID with planar dose map from Pinnacle system. For this purpose, the gamma evaluation method was used with a dose difference criterion of 2% of dose maximum and a distance to agreement criterion of 2 mm. Results and conclusion: The results obtained with EPID have been compared with the fluence distribution obtained with film. Relative to the film, the results are comparable and are within 3%. Excellent agreement was cm 2 water phantom was created With same MLC shaped seven found between TPS and EPID measurements with 95% of pixel counts individual plan was created.With calculation grid of 2.5 mm calculation falling with in the pass criteria. Amorphous -Silicon EPID offers time was performed. For dose profile study 1.25 mm grid was used for saving method for checking beam fluence for step and shoot IMRT calculation. Calculated dose profiles and PDD in treatment planning delivery. Though the absolute dosimetry information of the intensity system were compared with measured values. For comparison of dose map was not generated during the normalization process, the Gamma profile 80-20% penumbra was used. evaluation with TPS fluence can provide a efficient way to verify intensity Result and Discussion: PDD measurement was done perpendicular maps in IMRT. In addition to the fluence map verification, other checks to central axis. Because of divergent nature of radiation beam some like profile at low monitor units, leaf positioning of MLC leafs can also part of PDD was measured outside radiation beam at higher depth.
be performed using EPID. We found depth dose shapes accurately modeled by treatment planning system for depth greater than 2 cm in radiation field. Accuracy of O-04 treatment planning system in radiation field is well within 2% for all Evaluation of aperture based inverse planning for intensity depths. But noticeable difference is found when depth dose measured modulated radiotherapy outside radiation field at depth 15 cm and above. Measured depth Tushar Bopche, Kalpana Thakur, Ruchita Shah, Satish Pelagade, dose curves shows bulging outside radiation field for higher depths.
RK Vyas. Department of Medical Physics and Radiotherapy, Gujarat This bulging of curve increases as we move away from central axis.
Cancer Research Institute, Ahmedabad, India This bulging of curves could not model accurately by treatment planning system. Treatment planning system underestimate dose outside Introduction: To study the clinical efficiency of aperture based inverse radiation area. The profile penumbra sharpens is accurately modeled planning for intensity modulated radiotherapy by evaluating dose by treatment planning system. Calculated value of 80-20% penumbra volume histograms (DVH). from planning system well agrees with measured values. Variation in Materials and Methods: Aperture based inverse planning method depth dose curve outside radiation field needs further detail uses a predefined set of apertures. The apertures or segments can be designed by giving different margins to include target volume and to exclude critical structures. Some rules are used to establish aperture shapes. First a conformal segment that encompasses the entire target Fluence map verification of step and shoot IMRT fields using including critical organs if any coming in field is defined. Second, a amorphous -Silicon EPID field segment that conforms to the target but stops short of including Raghavendra Holla, TR Vevek, Preeti Deka. Manipal Hospital, Bangalore, the critical organs is designed. Third a field segment that covers the remaining portion of target without including the critical organ is established. There can be as many apertures as one can design with Introduction: Amorphous -Silicon flat panel detectors are currently several combinations of the margins to target and normal tissue. The used to acquire portal images with good image quality for patient number of such apertures is typically smaller than 100 for even the alignment before external beam radiation therapy. Although originally most complex cases. Based on dose constraints for targets and critical designed for imaging, the ability of the EPID to acquire rapidly a large structures, weights are determined for these apertures only. The dose two-dimensional array of digitized X-ray data is extremely attractive volume optimisation may discard many of the apertures which are not for dosimetry measurement as well. IMRT QA process can be tedious significant for desired dose distribution and end up with an even smaller investigation India and the film dosimetry verification on intensity map is very time consuming. The aim of this study is to test the feasibility of using an EPID system to independently measure the beam fluence during IMRT delivery. Materials and Methods: An Elekta Precise Digital accelerator with I View GT Amorphous -Silicon flat panel imaging system along with Scanditronix Omnipro IMRT verification software was used in this study.
Once the IMRT plan is acceptable clinically, the same plan is exposed over a flat surface phantom. All the beam angles and collimator angles are set to zero for simplicity. To study the impact of beam attenuation as encountered in clinical practice, EPID images were acquired with homogenous solid phantom of 5 cm thickness placed in the beam. In normal operation, the I View GT EPID continuously acquires images as a series of frames of fixed time (around 0.320 sec). At the end of the acquisition final 16 bit image is created by averaging all the frames, then normalizing to the highest gray scale region in the image thus discarding all dosimetric data. To prevent this the number of frames were recorded for each segment image. Each segment image is recorded separately, which carries individual renormalization factor called pixel factor. All the segment images are imported to Omnipro IMRT Software with original pixel factor. Composing all the segment final number of apertures. At last we can delete low MU segments and those segments which are having very small area. The lower limitation on MU and field size is dependent on treatment machine parameters. Finally plans are analyzed in 2D and 3D also with DVH.
Results and Discussion: The DVH analysis showed good target coverage and significant normal tissue sparing. The aperture based inverse planning significantly reduces both the number of segments and monitor units used for IMRT. This is accomplished without loss of dose coverage to for the targets and sparing of nearby critical structures. The large decrease in number of apertures reduces wear and tear of MLC system and lower monitor units results in reduced total body dose of the patient also. O-06 is the use of non-uniform intensity photon fields to produce dose distribution conformed to complex targets. Due to the complexity of the IMRT, the verification of dose delivery is decisive and clinical implementation of IMRT requires verifying the consistency between calculated and delivered dose distribution. In general, IMRT QA is broadly divided into machine and plan (patient) specific. Lengthy and tiresome procedure in plan (patient) specific IMRT QA is planar dose verification. Conventionally we do this with Film dosimetry. But the time spent to collect data with the film is quite long and influence of uncertainty is high in film processing. In the present work, the performance of Pixel Ionization Chamber array has been evaluated for imrt fluence verification. Materials and Methods: A pixel ionization chamber (PIC) array sizes were created with the mMLC having the leaf widths projected to the isocentre are 3 mm, 4.5 mm and 5.5 mm for the inner (14), middle (6) and outer (6) leaves, respectively and the photon energy of 6MV is used for all measurements. For this study, Relative scatter data, Percentage depth dose and Beam profiles have been measured and investigated by using Stereotactic Field Detector (SFD), farmer type ion chamber FC65G (0.6cc), mini-ion chamber CC13 (0.13cc), micro chamber A14 (0.01cc), RK chamber and conventional Kodak EDR2 films. For scatter factor measurement, test files were created using the Varian Shaper Program and data were acquired by using 0.6cc, 0.13cc, 0.01cc chambers, Stereotactic Field Detector SFD and Film. The scatter factors were measured for constant monitoring units (100 MU) at the depth of 5 cm and SSD kept at 100 cm for a matrix of (I'mRT MatriXX) from Scanditronix has been used for this study. The combinations of square mMLC fields Times Square jaw settings. The detector features a 24.4x24.4 cm 2 active area divided in 1020 normalized measured scatter factors were compared with Monte Carlo independent vented plane-parallel ionization chambers and can read values. Computer controlled Radiation Field Analyzer (RFA300) and out with a minimum sampling time of 20 ms per 2D field without SFD have been used to acquire percentage depth dose data. The mMLC introducing dead time. Each chamber has 4.5 mm diameter and 5 mm field size has been kept always equal to collimator jaw setting and the height; a distance of 7.62 mm separates the centre of adjacent PDDs for the mMLC square field sizes of 6x6, 12x12, 18x18, 24x24, chambers. The sensitive volume of each single ionization chamber is 30x30, 36x36, 42x42, 60x60, 80x80, 100x100 [mm 2 ] were measured. For this study, CT images of IMRT matrix and perspex The beam profiles have been acquired by using SFD, RK Chamber and phantom were acquired and test patterns of X-wedges, Y-wedges, Film for mMLC field size 6 x 6 cm 2 at the depth of 5 cm and SSD kept Dose well and two clinical IMRT fluency maps were imported into at 100 cm. PMMA Phantom has been used for film experiments. these phantoms as a separate plan in the Eclipse Planning system. All O-08-gopiraj Invivo dosimetry using TLD during pelvic treatment brass build up cap. For 6 MV beam, 1.5 cm water equivalent bolus A. Gopiraj, AK Mahant*, S Vinatha*, V Ramasubramanian # , M Rekha. material was used and for 15MV beam 3 cm bolus was used. The M. S. Ramaiah Medical College and Hosptial, Bangalore, *Radiation phantom used was cylindrical PMMA phantom of 30x30 cm 2 with a Safety Systems Division, BARC, Mumbai, density of 1.19 g cm -3 .
Technology, Dept. of Physics, Vellore, India Results and Discussion: Detectors used for in vivo Dosimetry are calibrated by measuring their response when placed on the surface of Introduction: The chain of steps in specifying the dose delivered to the phantom at the beam axis. Entrance dose calibration is done usually a patient undergoing radiotherapy includes several steps that may by calculating the calibration factor at reference conditions i.e., F cal.
introduce an uncertainty in the actual dose value. In clinical practice the reference conditions were set as a 10x10 cm 2 field size at the however this desired level of accuracy cannot always be achieved, due isocentre and SSD equal to 100 cm for each correction factor one to several sources of uncertainty. An overall check of the whole parameter is changed.
dosimetry procedure by in vivo dosimetry is therefore useful and sometimes even necessary if a high accuracy is required. Accurate in Entrance in vivo dose were computed by using the relation vivo dosimetry can be performed with entrance and exit dose CF i, measurements. Any discrepancy between the measured and expected is the entrance dose, R ent is the reading from the in vivo entrance dose can be caused by errors in patient set up in the number is the entrance dose calibration factor in reference of monitor units or in the irradiation time, beam out put variation etc. conditions and CF i is the various correction factors. In the current The measured exit doses also provide interesting information about study, correction factor was done for various Field size, SSD and Physical tissue thickness and tissue inhomogeneities through which the beam wedge, using brass buildup cap and bolus material for 6MV and 15MV passes. Using combined entrance and exit dose measurements, one photon beams. The intrinsic precision for MOSFET with brass build up can measure the modification of the overall transmission caused by cap in 6MV and 15MV photon beam shows a standard deviation of ± the presence of bone, air or soft tissue, as compared to the values 0.83% and ± 2.5%. The intrinsic precision of MOSFET covered with calculated assuming the patient to be water equivalent. The purpose water equivalent bolus material in 6MV beam was ±1.7% and for of this study is to derive and compare the mid plane dose from the 15MV beam it was ± 2.6%. The linearity of the detector for both 6MV measured entrance and exit doses for the patients undergoing pelvic and 15MV with both brass build up cap and bolus has a r 2 value of radiotherapy treatment. 0.9999. The standard deviation for field size correction factor between Materials and Methods: The external irradiation technique for the MOSFET covered with brass build up cap and bolus for 6MV and 15MV tumors in the pelvic region consists of a combination of an anteriorphoton beam was less than ±1%. However, the standard deviation for posterior (AP) and posterior-anterior (PA) open beam (two field SSD/ MOSFET covered by brass build up cap was higher than the standard SAD technique). For the two-field technique the dose is prescribed at deviation for MOSFET covered by bolus for both 6MV and 15MV beam. the point positioned on the central axis of the beams in the midplane The standard deviation for SSD correction factor between 6MV and of the patient. Patient treatments have been performed with Cobalt 60 15MV for MOSFET covered with brass build up and bolus was less than gamma rays generated by an ATC -C9 telecobalt unit. For each photon ±1%. The standard deviation of wedge correction factor for MOSFET beam TLD using appropriate build up material were positioned on the covered with brass build up cap and bolus for the wedge angle 15°, entrance and exit side of the patient during the treatment. In this 30°, 45° and 60° for both 6MV and 15MV was less than 0.1%, because study the entrance and exit dose of each field for five patients was the electron contamination did not play an important role in this case.
determined   between two taking into account the conformity to Planning target volume (PTV) and degree of complexity involved in delivery? Sliding Introduction: IMRT is an advanced form of 3D conformal radiotherapy window seems to be superior to segmental IMRT, but it requires more combining several intensity modulated beams to provide tumor dose quality assurance checks because of complex nature of treatment homogeneity and critical organ tolerance. The complex nature of IMRT delivery. Lesser complexity is involved with step and shoot delivery delivery imposes the need of a precise plan specific QA. In plan specific technique but PTV coverage seems to be inferior. Practically it is QA basically we do point dose measurements and 2D fluence important to keep delivery technique as simple as possible but the verification. In general, for point dose measurements we ensure that increase in complexity should be justified with improvement in dose the chamber dimension is less than field size. But in the case of non distribution. Modulation Index (MI) criterion given by S Webb can be uniform IMRT fields, each pixel has different fluencies. The objective used to compare the complexity involved in beam delivery in treatment of present study is to assess the best suited chamber and ionization plan. chamber volume effect for IMRT absolute dosimetry.
Material and Methods: Patients having carcinoma of head and neck Materials and Methods: All measurements were carried out with treated with Simultaneous Integrated Boost (SIB) IMRT with radiation our Varian CLINAC DMX C/D dual energy [6MV and 15MV] LINAC dose 60 Gy and 54 Gy in 30 fractions to PTV1 and PTV2 respectively equipped with millennium 26 pair DMLC. In this study, three cylindrical was selected for this study. Beam data of Varian high energy linear ionization chambers FC65G (0.6cc), CC13 (0.13cc) and A14 (0.01cc) accelerator CLINAC DHX (2300 CD) having 6 MV and 15 MV photons, are used. Prior to non-uniform field dosimetry, the output factors for equipped with Millennium 80 multileaf collimator (MLC) was used. field sizes from 1x1 cm 2 to 10x10 cm 2 were measured in SP100 water Millennium 80 MLC system has 40 leaf pairs having leaf width 1 cm at phantom with these three chambers and compared. For this study, isocenter. Eclipse treatment planning system with Helios (Varian Medical three pre-defined fluences like x-wedges with each strip width of 2 System) inverse planning IMRT software was use to create IMRT plans cm, 1 cm and 0.5 cm and also two fluences from clinical IMRT plans for dynamic and segmental techniques. The optimal fluencies were were imported to the ECLIPSE (3D/IMRT) treatment planning system converted to actual fluencies for sliding widow and by taking 5, 10 and as separate plans into a water phantom created. All the plans were normalized to deliver a dose of 100cGy at the isocenter at a depth of 5 cm in the water phantom. The planned IMRT fields were exported to the treatment unit through VARIS network and the plans were implemented on to the SP100 30x30x30 cm 3 water phantom and absolute doses at isocenter and ±2 cm lateral points were measured using the three ionization chambers and compared with ECLIPSE TPS calculated doses. Results and Discussion: In the output measurements, larger variations are found at smaller field sizes for FC65G 0.6cc farmer type chamber compared to the other two small volume chambers. The results indicate that the chamber dimension must be smaller that the field size. In case of IMRT field absolute dosimetry, dosimetric errors are found in all the three chamber measurements. For 2 cm x-wedge fluence, CC13 showed less dose deviation compared to that of FC65G and A14 chamber. For 1 cm x-wedge and 0.5 cm X-wedge fluences FC65G chamber showed less deviation compared to that of CC13 and A14 chambers. Chamber A14 showed less variation only in few measurements. Our results infer that the influence of the chamber volume effect in IMRT dosimetry was not appreciable. In small volume chambers the dose variations found may be due to positional errors and chamber sensitivity. In case of large volume chambers variations  the detector parallel to the surface. Detector is placed in a PMMA where ∆ p = abs(I p -I p-I ), I p is intensity of pth bixel, n is number of phantom and the beam cross section is only 25 micron x 500 micron. bixels in one dimensional beam, σ is SD of intensity values, N is the Simulations were performed using Monte Carlo code GEANT4. The number of changes between two adjacent bixels along leaf motion for GEANT4 Monte Carlo toolkit simulates the interaction of fundamental which ∆p > fσ and f = 0.01, 0.02, 0.03,………, 2. Z(f) is fraction of particles with matter. It is based on Object Oriented Programming and changes among adjacent bixels that exceed a certain fraction (f) of is composed of a collection of C++ classes, each representing a the SD. MI is the area under the spectrum between zero and F. particular aspect of the simulations process (geometry, tracking, Z (f)df visualization, etc.). Simulations were performed for lateral dose profile Results and Discussions: The global mean spectra for optimal and of a 100 keV single microplanar beam in the phantom. four actual fluences are shown in graph. From the graph it is seen that Results and Discussion: The dose profile shows asymmetry, a shift dynamic spectra is higher than optimal and S and S 15 spectra overlaps in the maximum dose point of the dose profile obtained for the Edge optimal spectra upto f < 0.4. Spectra of S and S 10 and S and S 5 are On MOSFET. By contrast, the dose profile at depth 7 cm in a PMMA lower than optimal for f < 0.75 and 1.25 respectively. This shows the phantom is symmetrical. The shift to the right of about 5 micron can inadequacy of S and S 10 and S and S 5 to describe low gradient be explained as related to dose enhancement effect arising from laterally regions i.e. presence of high steps with S and S and not required by scattered electrons from the Si body entering the SiO optimal fluence, leading to poor optimal actual coherence. However of laterally scattered electrons from the epoxy arising from poor the results of S and S 15 and dynamic technique are almost similar. electronic equilibrium. Conclusion: For highly modulated fluence maps the dynamic technique should be preferred when emphasis is on target coverage and dose Reference Introduction: Microbeam Radiation Therapy (MRT) is one of the frontier areas of research and an emerging radiation oncology modality, which utilizes highly collimated, polarized, extremely intense and tuneable synchrotron radiation beams over a wide range of energies for the treatment of brain cancer especially in pediatric cases. The aim of the MRT is to develop a method for radiosurgery of inoperable brain tumours like high-grade gliomas and paediatric tumours of central nervous system, where existing modalities fail to deliver the adequate results. Experiments with normal rat-brain have displayed unusually high resistance to necrosis when irradiated with such beams having dimensions of few tens of micrometers in width and delivered at skinentrance absorbed doses of 312 Gy to 5000 Gy, which appears quite

Physics, Anna University, Chennai, India
Introduction: Three-dimensional (3-D) radiotherapy treatment planning system derives the patient heterogeneity details from CT data. This study investigates the limitations of the dose calculation in heterogeneous medium by different correction methods employed in four commercially available treatment planning systems for 6 MV photon beams. Materials and Methods: Two phantoms were considered for this study. One is the in-house made layered Perspex phantom of size 24x24x12 cm 3 . An air cavity of dimension 5.5x5x4.5 cm 3 was created in the middle of the phantom to simulate the air-soft tissue geometry. Small holes of diameter 2 mm are made along the depth and cross profile of the phantom to accommodate micro Thermoluminicent Dosimeter (TLD) cubes for point dose measurement. The second one is the MED-TEC IMRT phantom, which is having a bone equivalent cylindrical shaped material of diameter 3 cm and length 5 cm to simulate the bone-soft tissue geometry. Facilities are provided to do the ionchamber measurement at the center and TLD measurements at different points of the high dense medium. Four commercially available treatment planning systems were used for the dose calculations in the

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above specified geometry. Three of the planning systems are using Pencil beam algorithm for dose calculation but handles the tissue heterogeneity in different ways, one is using Equivalent Tissue-Air Ratio (ETAR) and other two are using equivalent pathlength method correction methods. The fourth planning system uses the Collapsed Cone Convolution algorithm for dose calculations. A single beam configuration of field size 6x10 cm 2 was used so that, part of the beam passing through homogeneous soft tissue and part of the beam through soft tissue-air-soft tissue medium. For bone-soft tissue geometry field size of 6x6 cm 2 was used. Dose measurements were made using radiochromic film and TLDs in air-soft tissue geometry. Ion chamber and TLDs were used for dose measurements in bone-soft tissue medium. The Monitor Units (MU) calculated for a prescribed dose by generally applied: The first method is an extension of conventional treatment planning and is referred to as forward planning. [1] The second strategy, which we denote as inverse planning, usually starts with the optimization of fluence profiles from each beam direction by minimization of an objective function. Afterwards, sequencing transforms each optimized profile into a series of segments, which can be delivered with a multileaf collimator (MLC). The various dosimeric parameters like depth dose data, profiles, output factors, scatter factors, bulk leaf transmission and back up jaw transmission were measured for the purpose of modeling the 6mv photon beam for the treatment planning system used in this study. Results and Discussion: A. Dosimetric Analysis: The larger field sizes have higher PDD values for our dedicated system, the variation different planning systems were compared. Calculated dose profiles in PDD is limited to 3% between the 3 cm x 3 cm and 40 cm x 40 cm along homogeneous and heterogeneous regions were compared with open field sizes at depth of 10 cm. The percentage depth dose for the profiles measured using TLDs and radiochromic film.
wedged field sizes was measured and the variation found to be 4.2% Results: All the planning systems show good agreement with the between the 3 cm x 3 cm and 30 cm x 40 cm wedged field sizes at measured dose profile along depth and across the field in the depth of 10 cm. The OAR were computed from the beam profiles for homogeneous soft tissue region. But large deviations were observed 10 cm x 10 cm, 20 cm x 20 cm and 30 cm x 30 cm field sizes at 10 and between calculated and measured dose profiles in the cavity. All the 20 cm depths in the x (crossline) and y (inline) directions and were correction methods failed to predict the penumbral broadening of the found within ±0.2 mm. The relative output factors (OF) for different photon beam when it traverse from high dense to low dense medium.
field sizes and the scatter factor S c (r) for open field sizes were measured. It was observed that the deviation increases, for given energy and B. Quality -Assurance of dose calculation by measurements cavity dimension, as the depth in the cavity increases. A difference of B.1. Point dose calculations: The absolute point dose of the treatment 20-25% and 15-20% was observed for equivalent pathlength and ETAR plan was measured by using Head and Neck Cube supplied by correction methods respectively with measured profiles using TLDs Scanditronix Wellhofer. The same plan executed on machine with same and Radiochromic film. The collapsed cone convolution algorithm phantom by inserting 0.65cc active volume Farmer type ion chamber predicts the penumbral broadening with reasonable accuracy and it (FC65-G). The dose at isocenter was measured. The calculated and shows a difference of 4-6% with measured dose profile. There is a the measured doses were compared. difference of -1% between the calculated and measured dose using B.2. Isodose distribution comparison: The torso phantom (Scanditronix ion chamber in the center of the high dense medium. The TLD Wellhofer's) was used to compare the calculated and the measured measurements are also within ±3% of the calculated dose at different dose distributions. the film (Kodak EDR) was stacked in between the two slabs. Isodose distributions were measured using Kodak EDR film. Conclusions: Potential under dosage is possible because of the The exposed film was scanned with vidar scanner and the distributions penumbral broadening of the beam in low dense medium. Collapsed were seen through Omnipro IMRT software. The comparisons between cone convolution algorithm predicts the dose distribution in air-soft the calculated and the measured dose distributions were made within tissue geometry with good accuracy when compared to other studied Omnipro IMRT software system. [2] It is seen that the agreement between correction methods. In the case of bone-soft tissue geometry all the the calculated and the measured dose is within 2% in the high-dose correction methods show good agreement among them and with region. for clinical patient specific QA we specify 3% dose difference measured point doses. and 3 mm distance acceptance scaling criteria. [3] transmission and back up jaw transmission were 0.02% and 0.105%. Conclusion: Treatment-planning system configuration parameters Commissioning and quality assurance of a commercial must be measured precisely. The TPS calculated dose and the measured intensity modulated radiotherapy (IMRT) treatment planning absolute dose should not deviate more than 3% to ensure safe system preciseplan treatment. It is necessary to maintain strict criteria to compare SM Pelagade, KK Thakur, TT Bopche, DC Bhavsar*, RP Shah, measured and calculated values. The introduction of new analyzing RK Vyas*. Department of Medical Physics, *Radiation Oncology, The tools, such as DTA (distance to agreement) or G (gamma factor), Gujarat Cancer and Research Institute, NCH Campus, Asarwa, correlation coefficient can be useful to better quantify the comparison Ahmedabad -380 016, India between measured versus calculated dose distributions. [4,5] points.

The bulk leaf
The Corresponding author: Dr. S.M. Pelagade, E-mail: pelagade_satish@yahoo.com Introduction: The commissioning of the dose calculation algorithms of a treatment planning system is generally performed by entering the basic beam data into the system according to the methods and requirements described in the system user manual and by comparing the results of dose calculations with the entered data and with data that were measured specifically for this purpose. The purpose of this paper is to present our experience with the commissioning and QA of preciseplan treatment planning system with multileaf collimator (MLC) using step and shoot IMRT technique. Materials and Methods: A new dedicated intensity modulated radiotherapy (IMRT) unit Elekta's (precise) linear accelerator was used in this study. The blue phantom TM radiation field analyser was accurately positioned in the treatment room and left there for at least 2 hours in order to reach temperature stability. A 3D treatment planning system (TPS) for intensity modulated radiotherapy (IMRT) using a multileaf collimator (MLC) has been made available by elekta. Two techniques of computerized treatment planning for step and shoot IMRT are implementation of IMRT must not be underestimated. Every institution should adopt a QA protocol.  Introduction: Quality assurance (QA) of Intensity modulated radiotherapy (IMRT) using dynamic multileaf collimator (dMLC) is critical to ensure accurate delivery of optimized treatment plans. IMRT QA is divided into machine specific and patient specific tests. In this study we report results of patient specific tests for IMRT. Our patient QA procedure consists of an absolute dose measurement for all treatment fields in the treatment setup and film relative dose determination for adequate if the difference between the calculated and the measured dose was <5%. If the difference between measured and calculated dose exceeds 5% additional point dose measurement for individual field was also performed at 5-cm depth at gantry angle zero. For individual field dosimetry ±3cGy was passing criterion. Relative dosimetry was done by irradiating a Kodak EDR2 film placed perpendicular to the incident beam in a solid water phantom at 5-cm depth. Film dose distributions were analyzed using Omnipro IMRT software (Scanditronix-Wellhofer) and film scanner VIDAR DosimetryPro. For accurate alignment of the film on the densitometer four standard points were marked on the film along X and Y coordinates. As a department protocol, we verify only composite plans on phantom and not individual fluence. Films were analyzed with Gamma index the treatment plan. The tests performed revealed acceptable results. evaluation, DTA and isodose line matching. An acceptance criterion Materials and Methods: The equipment used are, Brainscan 5.3 for the planar dose was developed: 3% delta dose, 3 mm DTA, Spatial (BrainLAB AG, Germany) inverse treatment planning system (TPS), isodose lines > 50% must match within 2 mm. configured for 1-cm width Multileaf collimator (80 leaves), dual energy Results and Conclusion: Of the 20 evaluated plans 12 plans were Linear accelerator 2300CD, which are interfaced with Varis Vision within 3% dose variation, 3 plans were within 3-5% variation and 5 network (Varian, Palo Alto, USA). To start with IMRT plan an appropriate plans were above 5%. Individual field dosimetry at gantry angle zero arrangement of static beams is required for inverse planning. After for these 5 plans showed maximum variation of 2.75 cGy. Since QA defining the calculation parameters and constraints with respect to was performed in treatment condition, posterior oblique fields were target and organs at risk (OAR), the inverse planning optimization attenuated by treatment couch, which may be reason for variation generates 4 plans simultaneously with different Target and OAR more than 5%. Positioning the patient on extended carbon fiber couch priorities. It uses "Dynamically Penalized Likelihood algorithm'' for for daily treatment eliminated this beam attenuation problem. Gamma inverse planning optimization and pencil beam convolution for forward index evaluation method reveals on an average 95.4% of the data planning calculation. Among the four plans best-suited plan is selected.
passes the criterion with standard deviation of 3.58. The isodose line For QA, the solid water Phantom (Scanditronix-Wellhofer, Germany) matching was within acceptable limits. was scanned with 3-mm slice thickness. The dimension of Phantom was 18x18x18 cm 3 , which simulates head of the patient. For Pelvic O-15 simulation two lateral scatters were used. The ion camber insert was Entrance surface doses in majorly performed diagnostic placed at 5 cm depth. Once a plan is approved all dMLC files were X-ray examinations

O-16
124 AMPICON 2006 ABSTRACTS ORAL is possible only by measuring the ESD of patients. [1] ESD measurement in different radiology departments and comparison between them may be used to assess the overall condition existing in the radiology departments and implement corrective measures if needed. Chest radiography is the most common examination performed in radiology followed the lumber spine radiography. The present study is aimed at evaluation of the ESD in five major hospitals of Mumbai. Materials and Methods: ESD measurements were carried out by using TLDs CaSO4: Dy discs (6mm dia and 0.8 mm thickness) and LiF: Mg, Cu, P chips (3.2x3.2x0.48 mm). The TLDs were cleaned, annealed and packed in polythene pouches of 5 TLDs each. The pouches were placed on the patient at the central axis of the primary X-ray beam. The exposed TLDs were then read out using a calibrated TLD reader.
(ADC) maps of diffusion weighted images has been utilized. Multi Layer perceptron with one hidden layer has been utilized. The back propagation -gradient desent method with momentum has been utilized to train the multi -layer perceptron. For Self organizing maps, a novel segmentation algorithm based on the number of hits of the Best Matching Units (BMU) is proposed. The radial basis function has been trained with similar patterns used for both self organizing maps and multi layer perceptron. The results shows that the artificial neural network performs well in differentiating the tumor, edema, necrosis, CSF and normal tissues in reconstructed images of perfusion and diffusion weighted magnetic resonance images.
O-17 Calibration of the TLD reader was done using the calibrated ionization Effect on the breast entrance dose due to change in KVP and chamber Nero mAx 8000 in diagnostic energy region. A total of 50 the breast thickness patients were considered in each type of exam [ Table 1]. Set exposure Kanta Chhokra, V Jayalakshmi*, Reena Sharma*. RSD, Atomic Energy time and focus to film distance (FFD) in chest radiography were found Regulatory Board,*RP and AD, Bhabha Atomic Research Centre, ranging from 0.1 to 0.4 sec, 180 cm and for skeletal examinations, Mumbai, India 0.18 to 0.66 secs, 90-100 cm respectively.

Results and Conclusion: Large variations in ESD values have been
Introduction: The mean absorbed dose to the glandular tissue which observed for same type of X-ray examination in the different hospitals is most radiation sensitive is directly proportional to the breast entrance even though many times, the thicknesses of the patients were same.
dose. Therefore the aim of the study was to find the effect on breast ESD in each examination were found below the reference values entrance doses for varying breast thickness and at different kVp. specified by IAEA. The ratios of maximum to minimum ESD values are Materials and Methods: For the study a locally fabricated PMMA representative of the overall picture of the conditions existing in the phantom representing a breast of composition 50/50 was used. The various radiology departments. It was also observed that large variations breast phantom consists of 12 semi circular discs of diameter varying in ESDs were due to different procedures adopted by the hospitals from 9 cm to 21 cm and increasing in thickness by 5 mm at each step. e.g., X-ray equipment variability, operating conditions, imaging devices A dedicated indigenous mammography unit was used for exposures. A (type of screen-film combinations), processing conditions etc.
quality control check performed on the unit indicated the system confirmed to the acceptable limits. A calibrated external mammography We can conclude from this study that by proper selection of above procedures, dose to the patient as well as collective dose can be Segmentation of brain tumors in perfusion and diffusion A novel algorithm is proposed for performing the identification and segmentation of brain tumors in magnetic resonance images based on their vascular and cellular information provided by perfusion and diffusion weighted images. Different architectures of artificial neural network have been implemented in performing the segmentation of brain tumors and their performance has been compared. The architectures used are Multi Layer perceptron, Radial Basis function and Self organizing maps. These algorithms are trained to recognize and segment the brain tumors based on the vascular and cellular information provided by the reconstructed images of perfusion and diffusion weighted magnetic resonance images. The reconstructed images of perfusion weighted images such as relative cerebral blood volume (rCBV) image, time to peak (TTP) image and percentage of base at peak (PBP) image along with apparent diffusion coefficient   ionization chamber (Victoreen Model 6000-529) having volume 3.3 cc, diameter 4 cm and thickness 2.5 cm and energy response with in ±5% for half value layer in Al of 0.2 to 0.5 mm (16 to 90kVp) was used with calibrated Victoreen dose calibrator model 8000 Nero TM mAx for the purpose. The calibration of the measuring system is traceable to National Institute of Standards and Testing (NIST). A comparison and checking of the calibration of the system was done at Radiation Safety and System Division, BARC for energy range from 22kV to 40 kVp and the system performance was found to be with in ± 2%. The measurements were carried for phantom thickness ranging from 10 mm to 60 mm representing an equivalent of 1.1 cm to 7.5 cm compressed breast thickness of composition 50% adipose and 50% glandular tissues and for three different KVp normally used for clinical . m e d k n o w purposes i.e., 26kVp, 28kVp, 32kVp. The unit was set in the semi automatic mode where the kVp was manually selected and the mAs was automatically selected by the unit. All the entrance doses were normalised to 40 mm phantom thickness, which represents the standard compressed breast of 45 mm thickness and composition 50/50. Results and Conclusion: It is estimated that with increase in thickness of the breast, the relative entrance doses increases for the same kV. With increase in kV, for same breast thickness, the entrance dose increases up to 50 mm thickness. However for thickness greater than 50 mm, the relative entrance dose is maximum at 28kVp. These results are indicated in the Tables below. Since, the dose to glandular tissues which are most sensitive to radiation, is directly proportional to entrance surface dose, it is very essential, the radiologist selects proper kVp depending on the compressed breast thickness of each female patient undergoing mammography. As it has been observed that some mammography centers use only two kVps for all female patients in semi automatic mode where mAs is selected by the unit. This has resulted in higher mAs values and thereby higher breast entrance doses of 13mSv, where as 4mSv is recommended as the entrance dose per view film by ICRP. Materials and Methods: For this Matrix Laboratory language has been used. MATLAB codes have been developed. The computer algorithm operates on digitized mammography images. In the algorithm image has been read using MATLAB function. Complement of the image has been taken. The object to be segmented differs greatly in contrast from background images. Changes in contrast can be detected by operators that calculate the gradient of an image using the sobel operator which creates a binary mask using a user specified threshold value. Thresholding of the image to show small structures has been done. Compared to the original image there are the gaps in the lines surrounding the object in gradient mask. The linear gaps are made to disappear with the sobel operator. In order to make the segmented object look natural, we smooth the object by eroding the image with a

029, India
Introduction: Digital computers are now an integral part of medical imaging process. Images must be in a digital form to be processed by a computer. A digital image consists of a matrix in which each element is represented by a numerical value. The revolution in digital computer technology has made possible new and sophisticated imaging techniques. In mammography computer vision techniques have been used successfully to detect tumors on digital images. This technique therefore decreases errors in mammography interpretations. Image processing is the first step in most detection algorithms based on computer vision. Such processing allows signal to noise characteristics of certain findings in the image to be enhanced, while unwanted detail is suppressed. If images are taken with the digital camera then medical image analysis faces tougher challenge. Since medical images have a poorer noise to signal ratio. The spatial resolution and contrast between anatomical structures is often too low to be computed reliably using a standard image processing technique. Mammography X-ray is only diagnostically valuable if the resolution and spatial accuracy is sufficient to capture attenuation due to micro calcifications. In the current study our main aim is to study the computer aided detection system for breast cancer tumors.
diamond structuring element and close the threshold image.

Discussions and Conclusions:
The study demonstrated that computer analysis can render substantial help to the radiologist's screening efficiency. Computer vision techniques have the distinct advantages of being as reproducible due to the underlying computer code on which they are based. Most methods require that a number of empirical decisions be made regarding parameters that occur during the execution of the programs, such as filters characteristics of threshold level. Moreover, the computer aided diagnosis is based upon algorithm and hence impervious to day to day variations in human's interpretations. Such consistency in performance can be of great value to the radiologist, who operates in a very different environment. Further work has to be done to improve the accuracy and reproducibility of radiological images. Computer aided diagnosis has to come up in practical terms so that it may be used routinely by the radiologists in a clinical set up. This paper is a first step towards this direction.

O-19
Indigenous software for computer aided analysis of medical images using artificial neural network Neeraj Sharma, Amit K Ray, Satyajit Pradhan*, Shiru Sharma, Introduction: In recent years, considerable efforts have been made in computer aided diagnosis (CAD) of medical images to improve clinician's confidence in the analysis of medical images. Evaluation of medical images by clinician is qualitative in nature and may vary from person to person. Several techniques using multiple computer extracted features, pixel value based mutual information using Statistical approach, Syntactic or Structural approach and Spectral approach have The threshold value corresponding to 50% of confidence level was applied for segmentation. The programming of the algorithm has been done in MATLAB.

Results and Conclusions:
The software developed was first tested on different Markov textures to test the performance and the success rate achieved was 100%. The software was also able to detect distorted Markov texture cells impregnated with noise and the level of distortion.
The software was used in analysis of CT images of liver and brain to detect known abnormalities [ Figure 2]. The results were clinically evaluated and found in agreement with the radiological diagnosis. Finally it can be concluded that this software would be of great help in diagnosis and treatment. It would be an effective tool in auto contouring and evaluation of radiotherapy outcome by evaluating CT/MRI images. been tried. As a comparison between the above mentioned three approaches spectral frequency based method are less efficient, while statistical methods are particularly useful for random patterns/textures. For complex patterns, syntactic or structural methods give better results. Aims and Objective: The objective of developing the software is to achieve auto segmentation and tissue characterization. Therefore, we have designed and developed an algorithm for analysis of medical images based on hybridization of syntactic and statistical approaches, using Artificial Neural Network (ANN). This algorithm performs segmentation and classification in a similar way as is done in human vision system which recognizes objects, perceives depth, identifies different textures, curved surfaces or a surface inclination by texture information and brightness. Materials and Methods: Figure 1 shows the flow chart of the software. Bidirectional Associative Memories (BAM) network was used for feature extraction and classification of medical images. Associative network performs function similar to the human brain property of association and can recall Region of Interest (ROI) even in the presence of artifacts. In development of this algorithm ANN-1 was used for correlation feature extraction which is a specifically modified version of sBAM network and is capable of processing real coded, grey level phantom (Scanditronix Wellhofer, Germany) supported back side by phantom of plastic water (Computerized Imaging Referenced Systems, USA). DDs and TMRs were measured using 0.6 cc Farmer type ion chamber along with Dose 1 reference class electrometer (M/s Scanditronix Wellhofer, Germany). Inverse square law and conformity of depth dose characteristics of the beam was carried out for Focus   Axis Distances (FAD) from 1.0 m to 4.5 m. With phantom dimensions the accurate treatment to the tumor volume, verification of the dose is 90 cm x 34 cm x 30 cm and plane parallel chamber PPC 40 (Scanditronix a must. The radiation dose deposition pattern in radiotherapy is altered Wellhofer) entrance dose was estimated. Measured TMRs were verified by inhomogeneities present in body. The main aim of radiotherapy using exponential relation, accounting for scatter. treatment is to deliver maximum dose to the tumor volume and minimize TMR= exp {µ (d-dm)}. PSFR (1) the dose to the surrounding normal tissues and organs at risk. Therefore Measured DDs were compared with the earlier reports (Pogorsak 1985) to maximize the therapeutic benefit of radiotherapy, it is essential that and values used at another center in Poland for TBI (Instytut Onkologii, the absorbed dose delivered to all irradiated tissues in the presence of Marie Curie Center for Onkologie Gliwice). The dose outputs of the 6 such inhomogeneities be predicted accurately. The best method for MV beam for the maximum field opening were calibrated at 3.5 M and measuring the dose inside the patient is in vivo dosimeter. In this 4.5 M FAD using TRS 398 protocol of IAEA (2000) with 0.6 cc chamber study we developed indigenous inhomogenous and homogeneous at 10 cm depth in solid water phantom and Kq factor of 0.9919 and a thorax Indian average adult phantom fabricated with water equivalent factor 1.01 for using solid water phantom.
bees wax material for tissue and cork used for lung cavity. Finally the Results: Inverse square law was found valid for the large field, for dosimetry data's were compared with TLD and 3D TPS. The contour consists of body margin, lungs and spine. Applying measured values of TMR at extended distances are shown in Table 2.
magnification factor so as to get the exact contour of human thorax These values agree with calculated values using equation (1) within region magnifies the contour. The mould is prepared with thermocole. 3%. The calculated monitor units/ 100cGy using %DD and TMRs at The thickness of thermocole should be of contour separation. The depths 5 cm to 20 cm were in agreement within 3%. The measured contour is taken for 2 cm separation. Hence themocole with thickness absorbed dose values at dose maximum plane are Dose/MU = 0.0929 of 2 cm is taken. The exact contour is drawn on thermocole and then cGy/MU and 0.056 cGy/MU for FAD 3.5 M and 4.5 M respectively, cut. The thermocole mould is placed on nonstick sheet and the body which agree well with calculated values of 0.0925 cGy/MU and 0.056 margin and lung position are marked on it. The cork shaped as lung in cGy/MU at these distances. The entrance skin dose for magna field is the contour is placed over the marked position in nonstick sheet. Now 79.3% at 400 cm FSD compared to 50% for 10x10 cm field at 100 melted bees wax is poured slowly in the mould without forming air bubbles. Care is taken so that wax is not poured over the cork. The Conclusions: We have measured PDDs and TMRs for extended SSDs.
time is allowed to cool the bees wax then the mould is removed so As TMRs are independent of FSD, estimating dose to various planes that the beeswax with cork resemble the slice of the phantom. Like during TBI become easier. These physical parameters will be useful this the mould is prepared for all contours and slice of the whole for treatment planning in other institutions, if their 6 MV beam quality phantom is prepared. Then all the slices of the phantom are placed together in position, which resemble the exact human thorax phantom. Same procedure was repeated for making homogenous phantom except the lung cavity. To measure the point dose inside the phantom TLD capsules were used. In the central slice of the phantom several holes Podgorask EB, Pla C, Evans MD, Pla M. The influence of phantom were made at critical locations of the chest wall and lungs and also in size on output, peak scatter factor and percentage depth dose in the spine and heart position of the both phantoms. Fabricated FSD.
is comparable. Introduction: The human body consists of a variety of tissues and cavities with different physical and radiological properties. Most important among these, from a radiation dosimetry perspective, are tissues and cavities that are radiologically different from water, including lungs and bones. Especially thorax region has more inhomogenity than the other regions of the human body and it consists of different density material such as bone, soft tissue and lungs. Absorption of photons in lung tissue is different from water or soft tissues. The reason is different density, atomic number and electron density of these tissues. To deliver inhomogenous phantom was placed on the couch of Theratron Phoenix Co-60 machine. TLD capsules were placed in the central slice of the phantom such as Entrance, exit and midpoint, spine, media sternum, 12 points in lungs with various areas, 1 point in heart, 8 points in ribs. After placing the TLD capsule in the inhomogeneous phantom, it was irradiated for different treatment techniques in various conditions. Same procedure was repeated for the homogeneous phantom with the same treatment technique. We have three dimensional (3D) Plato version 3.31. The external contour of the thorax phantom was entered manually through digitizer in to the TPS in order to get an accurate reconstruction of the external contour of the phantom and also digitized lung cavities, spinal cord and various points to get the point dose. Similarly all the slices of inhomogeneous phantom were entered. The mass densities of the wax phantom and lung cavities filled by cork densities were also entered in the TPS. Similar methods adopted to enter the homogeneous phantom external contour, digitized in order to achieve an accurate reconstruction of the experimental geometry of the homogeneous phantom for the entire cavity of the thorax. The measurement points were marked with uncertainty of less than 1 mm for dose calculations. One of the point ® was fixed as a reference in the field to calculate the relative dose for each point. Reference point was fixed at the beam  is 3% for 4x4 cm 2 field size. This data is for 6MV photons with acculeaf, mMLC in siemens primus plus linear accelerator. In case of fixed collimator field size and different field sizes of mMLC i.e., from 4x4 cm to 10 x 10 cm, the output factor decreases to 6%. Conclusions: It can be concluded that the maximum reduction of 6% in dose delivery for 6MV photons with constant mMLC (4x4 cm) opening and varying secondary collimator field sizes from 4x4 cm to 10x10 cm is 6%. In case of fixed secondary collimator field size with variable field sizes of mMLC the maximum reduction in dose is 3%. The above two factors are due to backscattered radiation originating mainly from the secondary collimator with mMLC reaching the beam monitoring chamber. Also a maximum of 3% difference in backscattering is observed between mMLC and collimator. Hence we should take beam tumor volume.
radiotherapy treatments are acceptable for dose points and unit density measurements very carefully while using detachable micro multileaf materials. But the inhomogeneity inside the treatment volume will collimator because of the contribution of the radiation backscatter produce changes in the dose distribution. It depends on the density effect into beam monitor chambers. and the type of material and the traveling path of the beam. The thorax region is the main inhomogeneous region. Our study also reveals O-23 the same. Whenever planning to deliver radiotherapy treatment to the Megavoltage cone beam CT imaging in IGRT: Verification of cancer patient under inhomogeneous conditions inhomogeneity target and normal tissue location correction factor must be calculated to deliver accurate dose to the Vikram Maiya, Kumara Swamy, Sumit Basu, Sathiyanarayanan, Shrikant Deshpande, Janhavi Bhangle, Nirmal Kumar Babu. Department of Radiation Oncology, Ruby Hall Clinic, Pune, India Measurment of back scattered radiation from micro multileaf Introduction: Verification of target and normal tissue location is crucial collimator and secondary collimator jaws into the beam for 3D-conformal radiation therapy and IMRT because higher positioning monitor chamber from a dual energy linear accelerator uncertainty leads to larger planning target volume margin for tumor KR Muralidhar, Tirumalaiswamy, Shiyama, Madhusudhan Sresty coverage, which in turn increases normal tissue complications and Rajanesh, Pramod, Akraju. Indoamerican Cancer Institute and Research hinders dose escalation efforts. To improve treatment accuracy, Center, Road No 14, Banjara Hills, Hyderabad -500 034, India megavoltage cone-beam computed tomography (MVCBCT) using an E-mail: krmuralidhar@rediffmail.com electronic portal-imaging device is used. MVCBCT scans acquired on the treatment machine provide three-dimensional (3D) anatomic Introduction: The Photons and electrons backscattered from the information of normal tissues and tumors, overcoming a major limitation micro Multileaf collimator, upper and lower secondary collimator jaws of the conventional setup approach that employs two-dimensional (2D) give rise to a significant increase in the ion charge measured by matching of the bony anatomy identified from portal images. In this monitoring chamber. This increase varies between different accelerators. study, we have used MVCBCT, for verification of target and normal We have studied the effect of backscatter into the monitor chamber at tissue location.
6 MV photon energy for the Siemens primus plus linear accelerator.

Materials and Methods: 5 patients receiving IMRT for various
Materials and Methods: Variation of the output factor was first malignancies were selected for this study. 2 of the patients had cancers studied for variable field sizes of mMLC together with fixed collimator of the head and neck, 1 had malignancy of the mediastinum, 1 had jaws of size 10x10 cm 2 and also for fixed mMLC field size (4x4 cm 2 ) malignancy of the abdomen and 1 had malignancy of the pelvis. All with variable field sizes of secondary collimator. The output the patients underwent MVCBCT using ONCOR Impression LINAC before measurements were carried out at Dmax in a water phantom at central treatment execution. All these patients underwent MVCBCT, wherein axis. Backscatter radiation was analyzed. Results: In the first experiment the gantry rotated from 270° to 110° using 8MU protocol. After image it was noticed that the output factor is almost constant from 4x4 cm 2 registration, the offset/shift was calculated in the ant-posterior, cranio of mMLC field sizes by keeping secondary collimator caudal and lateral directions. The shift was secured after it was field size 10x10 cm 2 constant. The decrease in output factor observed compared with the planning CT scan. The necessary offset correction was applied.
Results: In all the patients, after co-registration of the planning CT to 10x10 cm 2 images having structures with MVCBCT images, the offsets were obtained. All the offsets within 3 mm were not corrected and those situations with offsets greater than 3 mm, the necessary corrections were done using the table movements.
Conclusion: The present study shows that MVCBCT is a useful tool that is used in verification of target and normal tissue location. This paves the way for highly conformal radiotherapy at greater doses delivered with increased confidence and safety.  Materials and Methods: The components used for the preparation of this gel was 5% gelatin, 3.5% BIS, 3.5% AA, 88% distilled water and 10 mM THP. The inverse planning for the selected cases was performed with the PLATO sunrise system and transferred to the CT scans of the gel phantom. The gel phantoms were irradiated with their long axis perpendicular to the central axis of the beam. The plane at which the laser beam of the optical scanner scans the gel phantom was measured as 4.7 cm from the base. The midpoint of this plane was positioned at isocentre for irradiation. The gel dosimeter was calibrated by irradiating the gels to 20 x 20 mm 2 fields up to a dose of 8Gy using 6 MV photons from the PRIMUS linear accelerator. Evaluation of the gel: Pre and post irradiation scans of the phantom were performed to obtain the attenuation measurements during two detectors, 9.8% energy resolution and center of rotation deviation of 0.412 mm and 0.1 mm. The photo peak was set at 140 keV with a 20% centered energy window. For CT, 20 cm QA Phantom containing 3 sections, namely first section as slice alignment, spatial resolution, CT scale and slice thickness section second section as low contrast resolution section and third section as water section each corresponds to single scan plane. SPECT/CT registration phantom was used for quantification of SPECT-CT registration.
Results: The reconstructed spatial resolution for LEHR with 157 mm and 210 mm radius of rotation was 7.3 mm and 9.2 mm respectively whereas for LEGP it was 9.2 mm and 11.4 mm. All SPECT images were of uniform intensity. There was no significant variation among two collimators at smaller radius of rotation but significant variation of reconstruction. The reconstruction was carried out using the 'iradon' uniformity among LEHR and LEGP was obtained at larger ROR. Signal reconstruction algorithm of the MatLab with 'Hann and spline' filters.
to noise ratio for 157 mm ROR were 0.206 and 0.201 for LEGPand The dose distributions obtained were compared with those from the LEHR but for 210 mm ROR these were 0.197 and 0.191 respectively. treatment planning system (TPS) using the Verisoft software from PTW, Contrast recovery for cold regions were 0.177 and 0.370 for LEGPand Netherlands. A quantitative comparison of measured and calculated LEHR (for 157 mm ROR) but were 0.363 and 0.63 (for 210 mm ROR) was obtained using the gamma technique developed by Low et al, respectively. Contrast recovery for Hot regions were 0.177 and 0.370 1998. Since the aim of the present study was to investigate the feasibility for LEGPand LEHR (for 157 mm ROR) but were 0.363 and 0.63 (for of using the gel for verification of complex radiotherapy plans, the 210 mm ROR) respectively. CT Uniformity (mean) was 0.3. CT Density plan obtained from the treatment planning system was taken as the (mean) for air, plastic and water were 1.18, 1132, 996.89.CT slice reference and the gamma indices were calculated. Each measured thickness was between 9 to 10 mm. In CT high contrast line separations point was evaluated to determine if both the dose difference and DTA were 3.0 line pairs per cm. Number of visible bar sets were 3. For low (distance to agreement) exceeded the selected tolerances 3% and 3 contrast, number of visible holes were 7 and smallest visible hole size mm, respectively. was 3 mm. The SPECT-CT image alignment was 1.87, 1.99 and 0.64 Results and Discussion: All the three cases showed a good mm in X, Y and Z direction respectively. The image quality of this comparison between the TPS and gel. The gamma distribution for the scanner is suitable for clinical imaging and quantifications. comparison of gel-TPS dose distributions passed the gamma criteria Conclusion: The image quality characteristics of integrated SPECT (3 mm spatial/3% dose deviation) in all regions except the low dose and CT scanner should be evaluated before it is used for clinical imaging. region and region near the container walls. The difference between The LEHR collimator can contribute effectively to a better resolution the TPS and gel distribution has been found to be less than 2 mm for than the LEGP collimator. The image quality of SPECT-CT becomes small tumors. The size of the gel container is the limiting factor since inferior as detector goes away from source. The image registration a deviation from the gamma criteria has been observed in the region must be calibrated for fusion imaging. near the container walls. This could be overcome by using larger gel phantoms. To obtain dose distribution, an absolute measurement of O-26 radiation dose calibration of each batch of gel is required. The time Software development for tumor volume measurement using required to verify the dose distribution for an IMRT plan is 20 minutes SPECT system including the time taken for post-irradiation scan.
NS Baghel, B Rajashekharrao*, S Dey**, RK Kher***, N Nair. Radiation Conclusion: Feasibility of using the PAGAT gel evaluated with the Medicine Centre (BARC), *Radiation Safety Systems Division (BARC), laser CT scanner for verification of IMRT treatment plans was **Computer Division (BARC), ***Radiological Physics and Advisory investigated. Both the gamma comparison and distribution comparison Division (BARC), Tata Memorial Centre Annexe, Parel, Mumbai -400 suggests that an accurately calibrated PAGAT gel evaluated with laser 012, India CT can be used as a quality assurance tool for complex treatment plans with high dose gradients.
Introduction: For estimation of tumor or tissue absorbed dose from radionuclide therapy procedures, determination of tumor or tissue volume is one of the most important radiation dosimetric parameter. Evaluation of image quality characteristics of integrated spect-Though, a variety of image segmentation techniques using SPECT have been proposed and described for tumor volume measurement, no CT Rameshwar Prasad, B Shetye, V Rangarajan, AM Samuel. Bio-Imaging Unit, TMH, Mumbai, India E-mail: rjhaji@yahoo.co.in Introduction: Integrated SPECT-CT has emerged as a new facility in the recent past due to its unique ability of providing both functional and anatomical images in a single imaging session. In this work image quality characteristics of SPECT and CT of integrated SPECT-CT scanner were studied. The effect of different collimators and different radius of rotation on spatial resolution, uniformity, noise and contrast levels were measured for each SPECT image. For CT, uniformity, density, slice thickness, high contrast and low contrast were calculated. The SPECT and CT image registration was also quantified for fusion imaging. Materials and Methods: For SPECT an acrylic cylindrical Jaszczak phantom, with insert of spheres measuring 9.5, 12.7, 15.9, 19.1, 25.4 and 31.0 mm diameter, insert of rods measuring 4.8, 6.4, 7.9, 9.5, 11.1 and 12.7 mm diameter and uniformity area was used. The phantom was filled with water and 15 mCi activity of Tc99m (TcO 4 _ ) was uniformly distributed. The images were acquired with a dual-head GE INFINIA HAWKEYE gamma camera having 1.523% and 1.536% integral uniformity, 1.072% and 0.85% differential uniformity in the CFOV for software however is available for this purpose. The objective of the present work is development of windows based software for volume measurement and its evaluation and validation using known volume spherical glass phantoms. Materials and Methods: A windows based software has been developed in visual C++ using Insight Tool Kit (ITK) library for 3D image segmentation and the Visualization Tool Kit (VTK) library for segmented image display. We have implemented three segmentation methods viz. manual fixed threshold, Adaptive threshold and optimal threshold. These three segmentation methods were inter-compared to determine the most appropriate technique for volume measurement. The basic approach of this software is to detect boundary of tumor/ object using a segmentation method and count all the voxels inside the boundary and multiply with the volume of voxels for calculation of total volume. In fixed threshold method, lower threshold was applied and all the voxels having gray level above the threshold were counted as part of object. In adaptive threshold method, a grey level threshold was found out from gray level histogram of the object which was a boundary of background and object voxels. In optimal threshold method, segmentation threshold was selected through an iterative procedure to separate the voxels into object and non-object

O-27
Reconstructed transaxial data was transferred in DICOM format to a networked PC and analysed using the developed software for volume Results: The Fixed threshold method is volume dependent and therefore requires prior knowledge of volume of object. To minimize the error in volume measurement, fixed threshold is higher in case of smaller volume than larger volume. Adaptive threshold method works well for larger volume and it over estimates for smaller volume. Optimal threshold method determines smaller and bigger volumes within acceptable limits of error. However, 99m Tc studies require attenuation correction on SPECT data. The percentage error in volume measurement was more for smaller volume phantoms than the larger ones for both the 99m Tc and 131 I phantom studies. Introduction: During last three decades, 4π gamma ion chamber has remained the pre eminent method for standardization of radionuclides. Though other methods such as defined solid angle, coincidence and anticoincidence counting have been used for specific radionuclides, the 4π gamma ion chamber measurements cover sources decaying by electron capture and positron emission. For routine calibration of radionuclides, radiation standards section maintains a high-pressure 4π Gamma ion chamber as secondary standards. The Centronic 20 th century IG 12 gamma ion chamber filled with argon at 2MPa has been recently calibrated with sources procured from Isotope Products Laboratories, Valecia having traceability to NIST, USA. Using

Source Holder Electrodes Liquid Source in Vial
Electrometer Printer (background) voxels. Spherical glass phantoms of different volumes ranging from 10 to 1000 ml were used to collect data on Siemens e.cam SPECT system using various radioactivity concentrations of 99m Tc and 131 I radioisotopes. To establish a relation between radioactivity concentration and exposure rate for different volume phantoms, surface exposure rate measurement on each phantom was carried out using a portable ionization chamber type of radiation survey meter. The data was acquired in 128x128 matrix and 64 steps in 360 o with minimum radius of rotation (ROR) using STEP and SHOOT method with Lowenergy high resolution and High-energy collimators respectively. The reconstruction was carried out using Fourier Back Projection (FBP) method using Butterworth filter. Scatter and attenuation correction methods were not applied to the data in the present work.

estimation.
Overall uncertainty (%) was then checked after normalization. The image co-registration was also checked with the help of a locally fabricated phantom. The CT numbers were checked weekly after imaging the CT phantom. Results: The Chi square value ranged between 0.8 and 2.5 for about a month after normalization. The normalization is done when the value of Chi square exceeded 2.5 or after a month whichever is earlier. The normalization is also done after any repair of the hardware or re loading of the software. The co-registration was also found to be acceptable. The CT values for water were within 0 ±3. Conclusion: To get the optimum image quality of PET/CT, it is necessary to daily check the chi square value for PET and weekly check of CT phantom images. The image quality was reproducible when chi square value were within the tolerance limit of <2.5. The co registration of PET and CT images was also acceptable all the time.
4π π π π π Gamma ion chamber: A secondary standard for the calibration of radio-nuclides Nathuram R. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai -400 085, India the calibration factors of 4π gamma ion chamber thus obtained, radioactivity measurements are traceable to the national primary standards, which is also maintained at BARC. The calibration factors obtained as a function of average energy of several isotopes are presented in this paper. Materials and Methods: Radioactive sources are widely used in several applications of nuclear sciences, medicine and engineering. In some of the applications, it is required to know radioactive strength accurately through measurements with suitable detector. However in measurements involving high accuracy, it is necessary to calibrate the detector with reference sources whose activity has been determined accurately. The RSS Division maintains secondry standards of radioactivity with the intention of providing and standardizing the radiation sources to the users of DAE and non DAE institution in the country. The secondary standard consists of Centronic IG12/A20, 4π or re-entrant high pressure ion chamber filled with argon gas at 20 atmospheric pressure connected to current measuring system. Circular lead rings about 5 cm thick shield the ion chamber. The current produced in the ion chamber is measured using an electrometer and the electrometer output is connected to a six and half digit Hewlett Packard multimeter. The multimeter is coupled to a computer using RS232 interface. Interactive program has been developed to read data at fixed time intervals, compute the average, correct it for background and store it on the hard disk for later processing and calculations. The block diagram of the secondary standard system is given in Figure 1. This system is calibrated against the primary standard, the 4πβ-γ coincidence setup for beta, gamma emitting radionuclides. Materials and Methods: The dose distribution has been calculated in the chamber and current produced was observed for a set of twenty around the model 6711 125 I source located in the center of 30 cm × 30 readings. Large number of measurements were taken to improve the cm × 30 cm water phantom cube by using MCNP4C code. statistical uncertainty. Each current measurement, which is corrected Results: The percentage depth dose (PDD) variation along the different for background, is an average of 20 observations taken within a time axis parallel and perpendicular to the source are calculated. Then, the period of 100 seconds. This current is denoted as the source current isodose points were found by interpolation from the relative dose curves. Is. Activity of the source is calculated using the following formula: Finally, the isodose curves for 125%, 100%, 75%, 50% and 25% PDD are presented.  Table 1. Also of fractions delivered varies from center to center, but at Pravara three shown against each isotopes, are the sensitivity factors of 4 gamma fractions of 7Gy each at weeks interval are delivered. One of the major ion chamber obtained with sources standardised on primary standards advantages claimed for high dose rate insertions is the opportunity to at BARC, Mumbai. The relative deviations in the response factors gain a better physical dose distribution by careful positioning and better measured for sources standardized at BARC and NIST are within ±5% packing for the short duration of treatment is required. Since only and is attributed to relative uncertainties in the standardistion. and is small changes in distance between applicator source and important well within range of experiental measurements. Accuracy: Most of anatomical structures such as bladder and rectum may result in large radioactive solutions having activity in the range of 10 kBq/g to 100 changes in dose delivered to these sites. Critics of HDR brachytherapy MBq/g, can be standardized by above technique with uncertainty of cite that patients should never be moved with an applicator in situ measurement in the range of ± 0.2% to ± 1% depending on the because of possible applicator movement and the potential for uterine perforation. So the purpose of the study was to evaluate changes in applicator position in-patients receiving high dose rate gynaecological brachytherapy as part of combined external beam and brachytherapy treatment for cervical cancer.   The importance should be given to individual planning for each high 20 2 5 6.
dose rate insertion where a fractionated treatment is required in order 80 3 8 7.
to accurately define the dose to the tumor area and more critically to 70 2 7 8.
Research Institute, Indira Gandhi Center for Atomic Research, ( w w w E-mail: kdevn@yahoo.co.in the cervix. This was then used to locate a standard fixed geometry Introduction: A high dose rate 192 Ir source is commonly used in intrauterine tube (tandem) and ovoid, three-channel applicator system brachytherapy. The recommended quantity for specifying the strength based on Fletcher style dosimetry. For each insertion standard antero of brachytherapy sources is air kerma strength. Air-kerma strength is posterior and lateral radiographs are taken with magnification marker specified in terms of air-kerma rate at the point along the transverse wires in the applicators. As per the ICRU 38 recommendations the axis of the source in free space. Primarily in-air calibration of the source bladder was localized using Hypaque within a catheter balloon and the is performed by the standardization laboratories such as National rectum using rectal wire. The AP and lateral films have been analyzed Institute of Standards and Technology (NIST), Accredited Dosimetry by taking measurements on the films to indicate reproducibility of Calibration Laboratories (ADCL) in USA and the National Research pelvic position, applicator position and relation to the ICRU bladder Council of Canada (NRCC). During purchase and installation the position of the ovoid source between insertions and the distance in the antero-posterior plane varied by a median of only 2-mm (range, 0 10 mm) The dose to the anterior rectal wall is reflected in the measurement between the ICRU bladder point and ICRU rectal point on the anterior rectal perpendicular to the bladder. The variation in this measurement is shown in Table 2 where median of 13 mm between dosimetry point and the anterior rectal wall. The measurements are shown in Table 1. Results: For all 30 patients it was possible to compare the measurements in Table 2    of neutrons, photons and/or electrons in three-dimensional geometry. Point detectors (F5 tally) and ring detectors (F5a tally) were used to compute flux at various points of interest, where 'a' can be either X or Y or Z-axis, the coordinates of the detector location. The decay photon energy spectrum of 192 Ir consists of 31 lines with energy ranging from 8.91 keV to 1.061 MeV. Total photon yield is 2.363 photons per decay. Each photon history originates at a random position and direction inside the source core. The simulations were done for 10 6 photon histories to obtain statistically acceptable results. Each photon history was traced down to 1keV, a default cutoff energy set by MCNP.
Results and Discussion: Initially the responses of the chambers were studied. The measurements were carried out placing the source inside a stainless needle as a source applicator. The inner and outer Target volume delineation and reconstruction of the implanted tubes were carried out from the CT datasheet using Plato-Sunrise treatment planning system. Dwell position in each catheter was loaded by giving an extra margin of 5 to 8 mm across the target volume. Four plans were generated for each patient. Basel dose points were defined i) at a single transverse plane and middle of the implanted volume and ii) throughout the implanted volume. Dose were normalized and optimized geometrically in both the cases and yielded plan 1 (P1) and plan 2 (P2) respectively. Another two plans were generated with dose prescription points defined along the catheter and in a plane 5 mm above or below the implanted plane. Dose was normalized and optimized on these points and this yielded Plan 3 (P3). Plan 4 (P4) was generated by employing graphical optimization on P3. Dosimetric diameter of applicator was 1.35 mm and 1.65 mm respectively, with a outcome from these 4 different plans were compared qualitatively and total length of 200 mm. The evaluated air-kerma strength of the quantitatively using the dose volume indices which include coverage GammaMed plus HDR 192 Ir source was found to be 23.31 ± 5% mGym 2 hindex (CI), relative dose homogeneity index (DHI), external volume 1 and 24.27 ± 5% mGym 2 h -1 with Farmer ion chamber and Well Type index (EI) and overdose volume index (OI). CI is the fraction of the chamber respectively, against the manufacturer stated value of 24.2 ± target receiving a dose equal to or greater than the reference dose, 5% mGym 2 h -1 . For Monte Carlo simulation, the source was designed DHI is the fraction of target receiving a dose between 100 and 150% with applicator and without applicator. The applicator was designed in of the reference dose, EI is the ratio of the normal tissue volume order to study effect of the applicator on the value of air-kerma strength outside the target receiving a dose equal to or greater than the reference of the source. The Monte Carlo (MCNP4B) computed air-kerma strength dose to target and OI is the fraction of the target receiving a dose of the source was 24.5 ± 2% mGym 2 h -1 and 24.6 ± 2% mGym 2 h -1 with equal or greater than two times the reference dose. A total dose of 36 the applicator and without the applicator, respectively. The percentage Gy in 9 fractions were delivered twice a day. differences are 3.7%, -0.29%, -1. 134 AMPICON 2006 ABSTRACTS ORAL tumour treatment. [1][2][3][4][5] In this paper, the dosimetric measurements were carried out on a newly developed skin patch using 32 P radionuclide for its potential use in superficial tumours. This patch contains about 37 185 MBq of activity, uniformly distributed on an area of 1.5-2.5 cm diameter sheets and can be easily applied on the affected lesion. Methods and Results: 32 P patch was prepared in Radiopharmaceuticals Division of Bhabha Atomic Research Centre, by adsorption of liquid 32 P on 1.5-2.5 cm diameter sheets of cellulose based absorber paper strips. Known quantity of 32 P activity in dilute phosphoric acid medium with a concentration ranging from 1.66-2.75 GBq/ml was dispensed at the centre of strip and was subsequently allowed to dry in air at room temperature. The dried strip was encapsulated within 40 microns thick plastic sheet. Sources of various empirical relation was obtained by the calibration of the films independently using a 60 Co radioactive source. D (Gy) = (NMOD -0.035) x 10 2 ……. (A) 4.72 The results obtained are given in Table 1. From the results, it is noted that the dose fall is very rapid towards the tissue as well as towards bone. The dose rate at 4 mm in tissue is nearly the same as at 2 mm in bone. There is a 79% fall in the dose rate at 1 mm and 93% at 2 mm with respect to the contact dose.
Conclusion: The dosimtery of newly developed 32 P patch source could be done with the help of GAFChromic films. The dose rate obtained from the above designed experiment will be helpful to the clinician in deciding the time of treatment and the dose to be delivered, if the strengths varying from 37 MBq to a maximum of 185 MBq each were activity in the patch supplied is known. From the dosimetry results prepared and activity level of ~ 37 MBq/cm 2 of the paper strip could obtained, it can be concluded that these patches can be used for the be achieved in final source form. The source was tested for non-leakage treatment effectively. The sources can thus be evaluated further for of radioactivity prior to dosimetric studies. The dosimetric their efficacy in animal models and could be developed as a method of measurements for this patch was carried out in a specially designed choice for treatment of superficial tumours. 166 patch for skin cancer treatment. International conference on having a 7 micron radiation sensitive layer on a 0.1 mm polyester future nuclear system. Wyoming: USA; 28 August to 3 September, base. The films were placed on either side of the source at different 1997. depths and exposed for pre-calculated time. After the stipulated time, 3. Chung YL, Lee JD, Bang D, Lee JB, Park KB, Lee MG. Treatment of the films were removed. There is a variation in the colour of the exposed bowens disease with a specially designed radioactive skin patch. film at different depths because of the penetrating power of the radiation Eur J Nucl Med 2000;27:842-6. and the density of the medium. The dose received by the exposed 4. Jeong JM, Lee YJ, Kim EH. Simple preparation of beta ray emitting films was recorded using a film densitometer, 24 hours after irradiation.     needles are replaced by nylon tubes. Interneedle distance is kept as following the ICRU 38 specification. In this study 37 intracavitary ring 1.5 cm and interplane needle is 1.2 cm. The whole implant procedure applications were analyzed and the dose received by the critical is done under general anaesthasia. Patient is shifted to CT scan for structures like the bladder and rectum have been reported.
imaging; 3 mm CT slices are taken. The images are transferred to TPS Materials and Methods: Patients with stage IIB, IIIA and IIIB cervical and body is contoured after 3D reconstruction. Tubes are digitized by cancers who had been treated with external beam radiotherapy [50Gy/ using 3-Dimensional saggital and coronal images with respect to each 25 # /5Wks] followed by HDR Brachytherapy [21Gy/3#/3Wks] were other. After digitization, tubes are loaded with HDR Ir-192 source by studied. After insertions of ring applicator, patients were simulated leaving about 1 cm margin from each end to avoid high skin dose. The and orthogonal radiographs were obtained. Rectal retractor was used source positions in the tube can be changed according to the clinical for every patient. Manchester system of dosimetry was used for the requirement. During planning, Geometrical Optimization allows computation of dose to point A and point B. The bladder was located conformal dose to the target and reduces dose to the surroundings using a Foley's catheter with 7cc contrast material and the bladder and helps produce a homogeneous dose distribution in a volume reference point was taken as per ICRU-38 specification. The rectum implant. Dose line Optimization implemented in Brachyvision 6.5 is was located by using rectal marker considering several rectal reference designed to account for critical structures. One of the features helps points. Treatment planning was carried out on 3D PLATO Brachytherapy the planner to alter dose values by pushing an Isodose line towards or software. The dose prescribed for each fraction was 7Gy to point A away from a structure boundary. This real time process may be and treatment delivered using MicroSelectron HDR (Nucletron) machine. Three ring diameters are available 26 mm, 30 mm and 34 mm, each has a 3 mm thick cap which is used wherever possible to increase the distance from the source train to the mucosa. Three tandem lengths are available 20 mm, 40 mm and 60 mm.The above rings and tandem are available with angulations of 30 degree, 45 degree and 60 degree.
The ring system was chosen for two reasons; firstly by turning it on edge one can insert it more easily through the introitus than in the case for colpostats and secondly since it clamps to the tandem, the geometry of the applicator is fixed. Results: The maximum and mean dose to the rectum and bladder reference points for two sets of applicator are shown in Tables 1 and  2. The maximum dose to rectum at point II was 78% and mean dose was 55.08%. Similarly for bladder maximum and mean dose were 79% and 62.51% respectively. The source loading was carried out diametrically opposite pair in ring, which is having more flexibility of source loading as per spread of disease and provides an added advantage. We generally do not do any optimization but by adjusting dwell position and dwell time weightage manually or graphically, isodose distribution is modified. Among all the ring applicator most frequently accomplished in any view, reducing the dose to critical structures or covering the entire lumpectomy volume with a margin about 5 mm all around with a particular dose line. At the same time high dose inside the target volume can be prevented and significantly reduced the dose near skin to avoid skin reactions. Plan is evaluated using natural DVH. The total dwell time is cross-checked with manual calculation as a part of pre-treatment QA.
Results: Ultrasound directed HDR breast implant is an extremely precise way to give radiation to the breast by applying proper optimization techniques to truly take advantage of the exquisite conformal dose capabilities of the after loading techniques.

Introduction:
In vivo dosimetry is the most direct and independent method for monitoring the dose delivered to the patient. Generally, in vivo dosimetry was well established and characterized for its use in external photon beam radiotherapy for the measurement of entrance and exit doses. [1] Although the calibration and commissioning procedures of an in vivo detector for the photon beam is similar to that of electron beams, only limited number of publications have been studied for their use in electron beams using TLDs [2] and semiconductor diodes. [3] This may be due to the large perturbation caused by the detector. Compared to TLDs and semiconductor diodes, MOSFET in collimating systems and blocks able to reach the MOSFET detector at the central axis. Hence the MOSFET has shown over response and the ratio of ion chamber to MOSFET decreases. In 15 and 18 MeV electron beams, these contaminating X-rays and the scattered electrons were absorbed by the WEHSBC. Since it is a dual bias dual MOSFET, no measurable effect in response was observed in the temperature range of 23-40 o C. The energy dependence of MOSFET dosimeter was within 2.9% for 6-18 MeV electron beams and it was 5.44% for 4 MeV. In the study of variation of sensitivity as a function of accumulated doses, MOSFET showed increased sensitivity up to 80 Gy and then decreases linearly. Pilot clinical study was also performed and suitable calibration and correction factors were applied. All the patient measured doses were within 5% with the calculated doses. The study showed that, the vivo dosimeters are being considered as alternative in vivo dosimeters.
MOSFET detectors are suitable for the in vivo dosimetry of electron This is because MOSFET has several advantages that include small beam radiotherapy in the energy range between 4-18 MeV. detector size, active area (0.04 mm 2 ), immediate reuse, immediate retrieval of information about the measured dose and its ability to References conduct multiple dose measurements. [4,5]  Although currently the quality audits are conducted to check the beam cGy. At 4-12 MeV, MOSFET showed large angular dependence in tilt output measured in the reference conditions but at the same time directions and lesser at axial directions. At 15 and 18 MeV, MOSFET certain other parameters relevant to the delivered dose also require with WEHSBC showed large angular dependence in axial directions checking and for this purpose IAEA/WHO has initiated work on a and lesser at tilt directions. This is due to the fact that increased path programme for quality audits in non-reference conditions. This length of the beam through WEHSBC causes the change in response laboratory had invited twenty hospitals for a pilot run in the nonof the MOSFET at axial directions. In the case of 4-12 MeV, MOSFET reference conditions; fifteen hospitals successfully participated in this was used without any build-up and it has showed significant SSD programme. The paper gives the methodology and the results of these dependence and the same was lesser for 15 and 18 MeV energies studies. when MOSFET was used with WEHSBC. As the SSD decreases, the Materials and Methods: The TLD material used was the LiF: Mg, Ti number of contaminating X-rays and the electrons scattered by the (TLD-100) powder filled in capsules similar to the ones used for the   quality audits in reference conditions. The parameters to be checked Radiation Safety to that effect is sent to the Kerala State Electricity are given below in the Table 1

. A TLD irradiation stand was supplied to
Board and power will be resumed only after getting a radiation safety all the participants, which can be used to irradiate single TLD in the  Table 1 to deliver a dose of 2 Gy taken care of. So far, 780 installations that satisfy the basic requirements to the TLD. The stand had a separate arm which could be fixed to the have been authorized by the DRS. This authorization is given for a stand for the simultaneous irradiation of three TLDs viz. at centre and period of one year. Recently the Government has also provided a vehicle off-axis at +5 cm and -5 cm as given in the S.No. (2) and (3). The TLD to DRS. in the centre in this case is to be irradiated to a dose of 2Gy and the Organisation: The DRS has the following technical personnel to dose delivered to the other two TLDs located off-axis has to be estimated manage the activities: from the beam profile data which is generally used in the clinical practice

Government of Kerala, Calicut -8, India
Colleges in Kerala to produce a radiation safety clearance certificate issued by the DRS. The MCI insisted for this after getting convinced of Introduction: This paper attempts to highlight the functioning of its importance and relevance, especially after the Supreme Court has Directorate of Radiation Safety (DRS) in the state of Kerala and started hearing the writ petition. Approval certificates of X-ray units emphasizes the significance of formation of such Directorates in other are issued by the AERB after getting report from the DRS. parts of the country in implementing the RPR in radio-diagnostic Conclusion: DRS in Kerala have made considerable progress in installations.
implementing the RPR in radiological installations. However, lot has to Formation of DRS: The Directorate of Radiation Safety (DRS) was be done in completing quality assurance tests, random checking of formed in the year 1998 by the Government of Kerala after proper discussions with the AERB and started functioning in the same year. A set of equipments needed for radiation safety and quality control programmes were also procured. The AERB has also authorized the DRS to exercise the powers conferred by Rules 29, 30, 31(a), (b), (c), (e) and (f) of RPR 1971 promulgated under section 30 of the Atomic Energy Act, 1962. Functioning of DRS: The DRS has identified 2560 Xray units and 120 CT scanners used in the state of Kerala. The number of IITV X-ray units identified was about 250 and dental units were around 100. Besides 20 DSA and CATH labs were also identified. Units satisfying the basic requirements of radiation safety were less than 10% before the functioning of the DRS. However, much improvement in the situation has taken place after the functioning of the DRS. The radiation safety requirements could be successfully enforced after the Government of Kerala amended the Electricity Act. As per the amendment, electrical connection to any new radiological equipment will be given only after the user producing a radiation safety clearance certificate from the DRS after incorporating the basic requirements of radiation safety in and around the installation. The power connection to the existing installation which does not have proper radiation safety status will also be disconnected if a letter from the Directorate of the installations, etc. The pace is slow due to non-availability of staff in full strength and shortage of funds, which may be overcome in the coming years.     Introduction: Cancer of cervix is the second most common cancer worldwide among women (IARC, 1992). Several treatments related protocols of radiotherapy have been followed over last few decades in its treatment for evaluating the response. These physical doses varying on the basis of fractionation size, dose rate and total dose need to be indicated as bio-effect dose (BED) to rationalize these treatments. There is a need for investigation in these areas and this study will address these aspects.  Results and Conclusion: The introduction of CWOSL reader system will facilitate alternative low cost indigenous OSL readers for dose measurements in radiation dosimetry and research applications. The reader parameters like stimulating light wavelength, stimulating light intensity, readout time, selection of optical filters, data transfer rate can be set by the user depending on the OSL sample under study. The OSL samples can be stimulated using CWOSL and LMOSL modes with a 470 nm stimulation wavelength with the light intensity > 100 mW/ cm 2 . The Figure 2 shows a typical CWOSL curve of an Al obtained using the above reader system. A minimum dose of 50 µGy could be detected for an indigenously developed α-Al using the above OSL measurement setup. The dose reproducibility for an absorbed dose of 10.5 mGy from a 90 Sr/ 90 Y beta source was within ± 5%. The alternate laser light stimulation source provision in the reader system increases the reader capability for the RandD applications. The OSL data is transferred to a PC through an RS-232 serial interface and stored in a user-defined file for later analysis. As the OSL data is stored in ASCII format, the data can be analysed by applying different algorithms using commercial software packages.
. Introduction: The KONRAD inverse planning system with Siemens Oncor dual energy Linear accelerator has been commissioned in our clinic for IMRT (Step and Shoot) treatment planning and delivery. The beam data required for commissioning were generated and relative and absolute dose measurements were carried out before clinical implementation. This communication reports preliminary results and perspective issues of commissioning this system. Materials and Methods: KONRAD uses the "Weighted quadratic (operating in 470 nm to 550 nm range) through an optic fiber. The user can select the LED cluster (blue or green) or the laser as a stimulating light source depending on the OSL samples under study. The electronic circuitry of the reader system is based on a single chip microcontroller (Phillips 89CC51) and the basic hardware consists of a 12-bit DAC (MAX 539), a 12-bit ADC (MAX 1241), MAX2323 for serial transfer of data to the PC, a high current source capable of supplying 700mA dc current to the LED cluster, etc. The stimulating light power at the sample position is recorded when a photodiode placed in the drawer assembly is brought below the PMT. The OSL output is recorded using photon-counting module. The reader is interfaced to PC through an RS-232 serial interface. The assembly language software for 89C51 microcontroller controls the entire operation of the reader on command reader system. This paper presents the development of a simple cost effective CWOSL reader system incorporating light emitting diode (LED) clusters as a stimulating light source and inexpensive optical color glass filters for measurement of OSL signal from the phosphor material and its application in OSL based radiation dosimetry. Description: The CWOSL reader system consists of two parts. The first part is comprised of lightproof drawer assembly for loading of phosphor material, stimulation light unit, photon counting module (for luminescence detection) and a drawer for housing optical filters. The second part consists of electronic circuitry, high current driver board for LED cluster, power supply units, PC connectivity etc. The block diagram of the OSL reader is shown in Figure 1. The system can be used for analysis of material up to 10 x 10 mm size. A super-bright LED clusters that yields a light output of 5.0 W carries out the optical stimulation of the samples. The light intensity focused on the sample position from LED cluster with peak wavelength λ p ≈ 470 nm or 530 nm and ∆λ ≈ 20nm. A GG-435 color glass filter is used to narrow ∆λ of the stimulating light beam and UG 1 filter to cut off the stimulating wavelength from reaching the PMT. An optical coupler has been provided on the light stimulation assembly to connect an external laser beam difference of prescribed and calculated dose distribution method" for the inverse planning algorithm to calculate the optimal intensity profiles (fields). The intensity modulated fields are divided into beamlets that can be delivered by means of sequence of leaf setting by the MLC. To ensure that what is delivered is same as calculated, the entire plan has been overlaid on the axial image set of the IMRT verification phantom. The entire treatment is delivered to the phantom and the integrated dose at predetermined points using the CC01 ion chamber is measured in the IMRT phantom (Scanditronix-Welhofer). The measured absolute dose and predicted doses from TPS were compared. Comparison shows excellent agreement (< 3%) at most of the measurement points. The film dosimetric QA of the IMRT is carried out by positioning the ready pack EDR2 film, at a particular axial image plane and delivering the entire treatment. The axial slice is in the Z-axis in the Konrad and at particular Z-level the film is placed. The dose profile in the DICOM format in that particular Z-level, where the film was positioned, is exported to the Omnipro-IMRT software. The measured fluence (or distribution) and the calculated are compared using the Omni Pro IMRT software. Excellent correlation (correlation coefficients > 0.97) was found for different axial plane between measured and predicted dose. Results and Discussion: Out of 20 patients the absolute dose varies from 0.24% (Min.) to 8.6%. The absolute dose variation exceeds 3% in 5 patients out of 20. The correlation coefficient (in case of Film Dosimetry) is ranging from 0.9715 to 0.9931 in all the patients. The gamma value in all the patients was less than 1.5%. The absolute dose variation in case of 5 patients was mainly due to the ionization chambers location was in the high dose gradient region. The Oncor Impression plus Accelerator is equipped with Optifocus 82 leaf MLC. Although maximum field size that can be covered is 40x40, the maximum length of the target organs that can be covered by the intensity modulated fields is 20x20 cm 2 . This is due to the over travel constraint of the jaws and MLC banks. The sequencer gives the option of profile smoothening, which smoothens the fluence pixels along the 094, *Department of Medical Physics, Tata Memorial Hospital, Mumbai 400 012, **Department of Radiation Oncology, ACTREC, Kharghar, Navi Mumbai, India E-mail: raj_resh@rediffmail.com Introduction: An accurate measurement of the surface dose of teletherapy units is a difficult task but it is important for quality assurance and clinical dosimetry. In many clinical situations, accurate knowledge of surface dose helps in deciding the optimum treatment parameters (i.e., beam energy, inclusion/omissions of bolus, techniques etc.) reduces the risk of sub-dermal fibrosis. The instrument of choice of these measurements is ideally extrapolation chamber but very few centres have this instrument. As a result many techniques with path in two ways namely 1D and 2D. Also planner can choose the correction and accuracy limit, such as fixed separation parallel plate number of intensity levels which finds deliverable solution which is chamber, TLD extrapolation technique as well as monolayer of TLD closer to optimal continuous distribution. Higher number of levels, powder have been successfully used for surface dose measurements. closer will be the deliverable solution to optimal continuous distribution, All these methods are laborious as well as time consuming. In the which further increases number of segments, introducing few low MU present study a simple method using Gafchromic EBT film (ISP segments. One important issue in Step and Shoot methodology is to Technologies Inc. USA) and flatbed documents scanner is used for the avoid low MU segments. The sequencer arrives at shapes in such a surface dose measurements. way all the shapes more or less have equal MUs. We choose optimal Materials and Methods: Surface dose measurements were carried intensity level, either 7 or 10 although highest level available is 15. On out on indigenously developed Bhabhatron telecobalt unit that have the treatment delivery side, it takes around 7 minutes for delivering 60 Co source of diameter 2 cm and source to collimator distance of 47.5 70 segments over 6 gantry angles arranged in the auto field sequencing.
cm. [1] The surface dose was measured for field sizes 5x5 cm 2 , 10x10 cm 2 and 15x15 cm 2 . Extrapolation technique was performed by irradiating a stack of five 1.5x1.5 cm 2 films placed in an appropriate Commissioning and clinical implementation of elekta MLC groove at the center of 30x30x3 cm 3 perspex plate. This perspex plate based IMRT with CMS XIO inverse treatment planning system containing the stack of EBT films was placed over the full scatter NS Shine, KV Rakesh, Joby Mathew, Satheesh P Prasad, Bhaskaran K phantom. The film stack was then irradiated for 4 Gy at the depth of Pillai. Department of Radiation Oncology, Amrita Institute of Medical maximum dose (d m ) using field size of 10x10 cm 2 at an SSD of 80 cm.

Sciences, Kochi, India
Similar procedures was followed for other field sizes. Film of size 1.5x1.5 cm 2 by placing at d m of telecobalt beam was also irradiated for 4 Gy to Introduction: This presentation details commissioning and clinical measure the output of the unit and reading of this film was used to implementation of IMRT with Elekta MLC and CMS XiO treatment normalize the reading of films in the stack. All the EBT film samples planning system. The "step-and-shoot" technique is used for this MLC-were evaluated 24 hrs after the irradiation. The films were analyzed based IMRT. Particular attention is paid to features unique to this using EPSON Expression 10000XL flatbed document scanner with hardware and software that are not addressed in general IMRT guidance ImageJ software. The thickness was measured using calipers and was found to 0.24 mm. Film density was also determined and it was found Materials and Methods: An Elekta Precise LINAC, equipped with to 1.34 mg/mm 3 . Using thickness and density values effective water 4,6,15 MV photon beams and 80 leaves MLC was commissioned for equivalent thickness of the Gafchromic EBT film was calculated to clinical usage along with CMS XiO 4.3 RTP system. Commissioning 0.32 mm. The surface dose for the field sizes 5x5 cm 2 , 10x10 cm 2 and process requires the verification of predefined parameters available 15x15 cm 2 were also measured using parallel plate chamber (model on the CMS XiO RTP System and the collection of some machine data. 23343, PTW Freiberg, Germany) by Gerbi et al method. [2] The machine data required are TSCFs down to a 1x1 collimator setting, Results and Discussions: Figure 1 shows extrapolated curve obtained PDDs down to 2x2 open fields, MLC transmission, Collimator from the exposed stack of films for three different field sizes namely transmission, Profiles at different depths for MLC formed field of size 5x5 cm 2 , 10x10 cm 2 and 15x15 cm 2 as a central axis percentage build 2x10. IMRT beam was modeled and checked the goodness of the MLC up dose measurement within the first few millimeters. The surface sigma parameter set in the beam modeling by comparing the measured dose measured using the parallel plate chamber by Gerbi et al methods 2x10 MLC profiles with TPS generated profiles particularly ensured literature. excellent penumbra agreement. QA procedure follows the recommendation of the AAPM Task Group No. 40 report. In addition,  Conclusion: The Physicist must be aware of leaf and jaw motion constrains that are unique to Elekta accelerator and how they are used in IMRT segment delineation by CMS XiO planning system. When these factors are considered in hardware calibration and beam  is also shown in the Table 1 for comparison. The effective point of measurement was assumed to be at the center of each film and thus the results for each film layer are quoted at half the water equivalent data sets were pushed to the treatment planning system through network. Structures such as Body (external contour), Planning Target Volume (PTV), Ipsilateral Lung (IL), Contra-lateral Lung (CLL), Heart, Contra-lateral Breast (CLB) and Liver were delineated on NB, DIBH, DEBH reconstructed 3DCT datasets. Conventional tangential fields were placed on the 3D-CT dataset by isocentric technique with matching posterior field borders. The isocenter is placed at the center of mass of the PTV with the help of the tool available in the planning system. For each patient, simple tangential field plans were created for the three different CT data sets and DVH analysis were performed for the following structures: CTV, heart, ipsilateral lung, contralateral lung, liver and contralateral breast. Parameters such as V50 (volume covered by dose >50Gy Isodose) for heart, ipsilateral lung, liver, V30 (volume thickness, i.e., 0.161 mm. Due to the nonlinear nature of photon build covered by dose >30Gy Isodose) for heart, V20 (Volume covered by up characteristics, a second order polynomial curve extrapolation was dose >20Gy Isodose) for ipsilateral lung were noted down. used as the line of best fit to determine surface dose. Impact of different breathing conditions on the dose to Introduction: Yttrium Aluminum Garnet (YAG) is a well-known surrounding normal structures in tangential field breast phosphor material with a wide variety of applications. However, the dosimetric applications of YAG for medical dosimetry using optically R Prabhakar, T Ganesh, M Pandey, PK Julka, GK Rath, RC Joshi, AK stimulated luminescence (OSL) techniques have not been reported Bansal, PS Sridhar. Department of Radiotherapy, Institute Rotary Cancer so far. The recent report of OSL properties of YAG exposed to beta Hospital, All India Institute of Medical Sciences, New Delhi -110 029, radiation [1] has generated a lot of interest for its dosimetric properties in environmental and high-energy dosimetry. The present paper E-mail: rampraba@rediffmail.com discusses the YAG as a new phosphor material for its possible use in the high-energy dose measurement based on OSL technique. Introduction: Treatment of early breast cancer by radiotherapy after Materials and Methods: The crystalline YAG powder was conservative surgery improves the local control, however improvement synthesized using the nitrates-urea solution combustion reaction [2] in treatment outcome must always be balanced with the potential risk and given a pre-irradiation annealing treatment at 1000°C for 1 hr to of long-term complications such as late cardiac mortality and radiationremove the thermal stress and impurities during its preparation. The References 1.

2.
radiotherapy India induced pneumonitis. The challenging parameters, which interfere in achieving the treatment outcome and complications, are organ motion and setup-errors. Organ motion is one of the serious concerns in radiotherapy and with the introduction of newer treatment approaches like image guided radiotherapy; the importance of organ motion in treatment planning has been highlighted. In this study an effort has been made to study the dose to surrounding normal structures such as heart, lung, contralateral breast (CLB) and liver due to three different voluntary breathing conditions. Materials and Methods: Thirteen patients with early breast cancer who underwent conservative surgery: nine left-sided and four rightsided breast cancer patients were selected in this study. Prior to imaging, the patients were trained to hold their breath in deep inspiration and deep expiration. The area of CT scanning included the superior (cranial) and inferior (caudal) border of the field marked by the radiation oncologist with an additional margin. Spiral CT scans were performed in Siemens Volume Zoom CT for all the three breathing conditions viz. Deep inspiration breath-hold (DIBH), normal breathing hold (NB) and deep expiration breath-hold (DEBH). The average time for which the patients were asked to hold their breath was 15-18 sec. The CT image YAG samples weighing 20 mg each were irradiated to 1.25 MeV photons using a 60 Co teletheraphy machine (Theratron 780E) to an absorbed dose in the range of 1 Gy to 1 kGy using in a PTW water phantom at a depth of 5 cm. The samples were also exposed to high-energy X-ray photons (6 MV to 18 MV) for an absorbed dose of 1 and 2 Gy in a tissue equivalent phantom at a depth of 5 cm using linear accelerators (Varian Clinac 2100C and Clinac 2100 CD). The  OSL measurements were done using photon-counting module in a programmable OSL reader interfaced to PC through an RS-232 serial interface. The samples were stimulated using continuous wave (CW) OSL mode with a 470 nm stimulation wavelength (light intensity > 200 mW/cm 2 ). Results: The OSL response of the YAG phosphor for the 60 Co in the dose range of 1 Gy to 1 kGy is shown in Figure 1. The YAG is found to be a sensitive OSL phosphor having a linear dose response in the dose range upto to 1 kGy. The phosphor was also found to have an energy independent response for photons in the range of 1.25 MeV ( 60 Co g-rays) to 18 MV (X-rays) as evident from Figures 2 and 3. The normalized and absolute OSL response of YAG for variable photon energies for an absorbed dose of 2 Gy is shown in Introduction: CT based dosimetry provides a clinically realistic evaluation of interstitial implant as compared to traditional orthogonal radiograph technique. In this study dosimetric outcome of radiograph and CT based planning of multi-catheter intestinal implant used for Accelerated Partial Breast Irradiation (APBI) were compared using different dose volume indices. The potential of interactive isodose optimization algorithm was tested for improved tumor coverage. Materials and Methods: Intra-operative placement of flexible nylon tubes were performed on twelve consecutive patients of early stage breast cancer using the Paris system. For each patient an enface radiograph and axial CT images were taken and dosimetry was carried out on Plato Sunrise TPS. Lumpectomy cavity, CTV and ipsilateral breast were delineated on axial CT images following RTOG 0413 guideline. Catheter reconstruction was done on CT images. For each patient three plans were generated using active loading length  O-50 over 0.51 and 0.60 of P1 and P2 respectively. Conclusion: Dosimetry based on the active length measured from X-ray provides excessive irradiation of normal breast. Interactive graphical optimization allows the shaping of prescription isodose to the shape of target at the cost of high dose volume and dose inhomogeneity. Use of dose volume indices allow quantitative evaluation of different plans and can be use as a tool to correlate dosimetry with clinical outcome.
Study of X-ray attenuation properties of indigenously developed shielding materials made of red mud and fly ash with barium compound measurements were carried out first for lead sheets of varying thickness and transmission curve was plotted. Similar measurements were carried out for each sample of red mud slab to find percentage transmission. Using transmission data of each sample, linear attenuation coefficient (µ) and half value thickness (HVT) are computed.
Result and Conclusion: The X-ray beam attenuation characteristics in terms of HVT for different red mud slabs at 100 kV energy of X-ray has been computed and compared with HVT's of conventional concrete and lead materials and are shown in Table 1.
The HVT values of few red mud slabs are slightly higher than the HVT values of lead and HVT values of red mud slabs are significantly less than the HVT values of concrete for 100 kV X-rays which is Aarti R Kulkarni, Neeraj Dixit*, N Kadambini Devi, VK Shirva, SP Agarwal.
used for medical diagnostic applications. Conventionally used lead Radiological Safety Division, Atomic Energy Regulatory Board, Mumbai, is characterized by high toxicity in production and recycling and *Radiological Physics and Advisory Division, Bhabha Atomic Research causes environmental pollution. Iron, barium and titanium are non-Centre, Mumbai, India toxic and can be used effectively for shielding against X-rays as the next choice. The red mud generated in aluminium industry contains Introduction: Different structural shielding materials are used in fairly high quantity of iron oxide, titanium oxide and aluminium the construction of X-ray installations and radiation facilities for the oxide and hence composition of Red Mud with barium compound safety of radiation workers and general public. Currently concrete, shows efficient shielding for X-rays. It appears from the brick and lead are used as structural shielding materials (brick is measurements that the tested shielding materials can be used for used only up to diagnostic X-ray energy range). We have studied the various shielding applications in diagnostic X-ray and CTthe radiological properties of slabs of different samples of red mud installations as well as for protective accessories used in radiation and fly ash (developed with composition of barium compounds) [1] facilities. generated from aluminium industry waste. The red mud based shielding materials confirm to the requirement of compressive Acknowledgement: The authors are thankful to Shri S.S. Amritphale strength and impact strength as specified by Indian Standard for and Shri Avneesh Anshul of Regional Research Laboratory, Bhopal for cementious shielding materials and ceramic tiles. [2] Red mud is the providing the red mud samples for this study. waste generated during aluminium production from bauxite. It is reported that production of 1 tonne of metallic aluminium generates Reference about 2 tonnes of red mud. This paper presents the comparative study of X-ray attenuation properties of red mud based shielding 1. Amritphale SS, Anshul A, Chandra N, Ramkrishnan N. A novel materials with the conventionally used shielding materials such as process for making radiopaque materials using bauxite-Red mud. concrete and lead. Methods: Attenuation characteristics of Red mud J Eur Ceramic Soc 2006;10:1016/j.jeurceramsoc.2006.05.106. slabs of size 12 cm x 12 cm (of different compositions with barium compounds) and lead sheets were studied using Polydoros LX X-O-51 ray unit (total filtration 4 mm of Al). Unfors make solid state detector Current status of beta dosimetry for personnel monitoring TLD based (sealed silicon detector) dosemeter was used to measure badge: Response for disc type and tape type cards based on the incident and transmitted dose (I 0 and I t ). Collimated X-ray beam CaSO 4 : Dy teflon of size 10 cm x 10 cm at target to dosemeter distance of 100 cm K Srivastava, G Varadharajan, S Chatterjee, AK Bakshi, RK Kher. was used and the slabs were inserted between the target and Radiological Physics and Advisory Division, Bhabha Atomic Research dosemeter to measure the transmitted dose. Transmission Centre, CTCRS Building, Anushakti Nagar, Mumbai -400 094, India    Introduction: Accurate measurement of beta radiation is important Result and Discussion: Table 1 gives the TL response and relative in personnel monitoring as significant number of workers receive beta response (normalized against the response of bare card) for two doses specially those from the nuclear industries and research types of TLD cards for different irradiation geometries using all the organizations. However, thermoluminesce dosimetric systems gives three beta sources. It is evident that both TLD systems are not highly energy dependent response for beta radiation. Several methods suitable for measurement from Pm-147 source, as TL readings are have been proposed to minimize the beta energy dependence and in the range of background counts and lack any pattern to enable the improve the dose estimation of beta doses. An ideal beta dosemeter dose estimation. However, It was found that when tape card was will be ultra-thin TL dosemeter made up of tissue equivalent material exposed with tape side facing the source, TL counts were more by such as LiF covered by ~ 5 mg.cm -2 thick tissue equivalent filter to factor of 1.01, 1.19 and 3.85 for Sr-Y-90, Kr-85 and Pm-147 respectively. measure Hp(0.07), which is an internationally accepted quantity for Thus the presence of mica sheet as anti buckling device deprived the beta dose reporting (ICRU 47). However, ultra-thin TL dosemeters advantage of thinner dosemeter. Table 2 gives the Disc Ratios under have certain limitations as they have high detection threshold, require different filter regions for Sr/Y-90 and Kr-85 source whereas for Pm very careful handling during readout, high quality control at production 147 these ratios are not significant and hence not provided. level for sensitivity variation and sophisticated instrumentation. In Conclusion: This study was undertaken as base work for the India, presently a three element CaSO 4 : Dy Teflon disc (0.8 mm or development of thin dosemeters to cover wide beta energy range. It thick) dosimeter is being used for photon as well as is evident that present system is not suitable for beta energies less beta dosimetry since 1978. [1] The Badge is worn at either chest level than 0.5 MeV. In order to cover the lower beta energies and improve or wrist/head level depending upon the working condition. Each Disc the accuracy in dose estimation it is necessary to develop of thin is prepared by cold pressing an individually weighted fixed mass of dosemeter. uniformly mixed CaSO 4 : Dy and Teflon in ratio of 1:3. In order to make the preparation procedure less cumbersome and to take References advantage of thin dosemeter, a skived tape type dosemeter was developed in 1992. [2] A single tape element (51 mm x 17 mm x 0. 4 1. Vohra KG, Bhatt RC, Bhuwan C, Pradhan AS, Lakshmanan AR, mm i.e., 80 mg. cm -2 ) was used and an anti buckling device (mica Shastry SS. A personnel dosimetry TLD badge based on CaSO strip 25 mg.cm -2 ) was provided to avoid any buckling during heating.
Dy Teflon TLD discs.     Obtained from BJR along central axis Results: We have exposed the film for 10 cGy and then we have divided whole film into sector of 1.7 cm, measurements has been taken at the middle of each sector. If we compare the highlighted points of Table 1 with values shown in Table 2, we can see that film scanning data shows better variation in output compared to the values obtained by Secondary Standard dosimeters for the same distances. Discussions: Clarkson's technique is not practical for manual calculation. Day's method is found simple for manual calculation. K Q factor, which is simply ratio of the output at any point within the field to the output at the centre, also K Q is determined in air for the primary beam. Once it is generated rest of the calculation is simple and found useful for percentage depth dose which can be calculated at any point within the medium or outside the field limit by using Day's method.

Conclusions:
i. The values of K found from minimum 0.8327 to 1 maximum for Q 30 x 30 field size and are reproducible on other machines too Materials and Methods: Monte Carlo calculations: Point source-based dosimetry data are still in use for realizing dose distributions in water around cylindrical brachy photon sources. Methods such as quantization and Sievert intergral make use of these data. Dose rate to water at radial distance, r in water medium due to a point photon source in water can be calculated from the following relation: where S k is air-kerma strength of point photon source expressed in wat is the ratio mass-energy-absorption coefficient ρ air of water to that of air and f (r) is dose ratio function that accounts for combined effect of attenuation and energy absorption build-up factor in water. The ratio of water-kerma in water, K w,w (r) to water-kerma in free space, K w,f (r) gives f (r). The latest published study is calculation of point source-based radial dose function, g(r) and reference doserate in water (dose-rate at 1 cm) in a 50-cm radius water for 137 Cs,

AMPICON 2006 ABSTRACTS ORAL
Results and conclusions: Film response curves for both EDR2 and EBT films are shown in Figure 1. This figure clearly shows the sensitivity of the EBT film to be considerably lower across the entire to agreement parameter, gamma. Gamma maps for both EDR2 and EBT films taken in the coronal plane are also calculated. The low dose discrepancy is likely also a result of low sensitivity. The low sensitivity required that large scaling factors (based on ion-chamber measurements made in the high dose region) be applied from this study the low sensitivity of EBT, the shape of the response curve The iso-dose curves and film profiles taken with both EDR2 and EBT films in the coronal plane. This shows good agreement between the calculated and measured dose distributions in the high dose prostate patient using external beam therapy (EBT) radiochromic film. The recent development of intensity modulated radiotherapy (IMRT) using a linear accelerator (linac) offers a major advancement in radiation therapy by allowing for more conformal dose distributions to be delivered to target volumes; thereby allowing for greater sparing of normal tissues. Tomotherapy represents the next step in IMRT treatments. Tomotherapy, which literally means "slice therapy", uses a megavoltage linac mounted on a CT-like ring gantry which rotates and delivers fan beam of radiation as a patient is translated on a treatment couch through the bore of the machine. Intensity modulation is achieved using a binary multi-leaf collimator. In addition, a bank of megavoltage-CT (MVCT) detectors is located on the gantry, opposite the linac, to provide onboard MVCT imaging capabilities. While both conventional IMRT and Tomotherapy treatments offer significant advantages in terms of the ability to shape delivered dose distributions to the target, they do so at the cost of increasing the complexity of treatment delivery. This increased complexity in turn requires more rigorous and precise methods of quality assurance to ensure that the dose distribution delivered by the machine agrees with the distribution calculated at the time of planning. Current methods for the verification of the dose delivery of the tomotherapy involve delivering the treatment beams from an accepted patient plan to a solid-water phantom containing radiographic film(s). The use of radiographic films however presents various difficulties, including a strong deviation from tissue equivalence, cost escalation and time-consuming film processing. In order to avoid these difficulties, this study seeks to asses the potential of EBT radochromic for the EBT and scaling to ion-chamber readings taken in the high dose region rectifies the problem in the high dose regions, but fails to do the same for the low dose regions.   film for the verification tomotherapy dose delivery. Materials and Methods: Both EDR2 and EBT films were characterized by their response to a series of nine known dose values ranging from 0-400 cGy delivered with a Varian Clinac 2300 linear accelerator. The treatment plan for single patient, previously treated for prostate cancer with Tomotherapy, was selected and the treatment beams from the selected plan were applied to a cylindrical solid-water phantom, allowing for the dose to solid-water to be calculated. The treatment was then delivered a total of four times, twice with EDR2 films placed within the phantom and twice with EBT films. For each type of film, treatments were delivered with the films oriented in first the coronal and then the saggittal plane. Additional measurements were made during each treatment delivery using an A1SL ion chamber. The ion-chamber measurements were used for both point dose comparisons as well as a means of scaling the relative film values to an absolute dose measurement. Following treatment delivery, films were allowed to wait overnight before being developed and then scanned using a Vidar VXR-16 Dosimetry-Pro Film Scanner. The scanned films were then transferred to the Tomotherapy treatment planning system for analysis.  corrected. In view of above consideration, the present study was carried out to investigate the response/behavior of the personnel monitoring TLD badge used in our countrywide personnel monitoring Materials and Methods: The TLD badge used in this study is same as is used in our countrywide personnel monitoring programme. For this study, the TLD cards having spread in sensitivity less than 5% were used. The measurements were carried out with siemens primus high medical linear accelerator having dual photon beam energies (6 and 18 MV). The TLD badges were kept at phantom (virtual water phantom) and were exposed to three different doses at 7. The buildup material used for the purpose was virtual water (tissue equivalent material) slab of different thicknesses. The exposed TLD's were read on a well-calibrated automatic hot gas TLD badge reader. Result and Discussion: It is well established that with the increase of photon energy, the depth at which maximum dose is delivered increases from almost 15 mm for 6MV photon beam energy to almost 30 mm for 18MV photon beam energy and this fact is confirmed with ionization chamber as well as with the TLD badge. It has also been found that the TLD badge worn by a radiation worker in highenergy field can sometimes lead to a misleading radiation patterns. This is likely to be encountered with those TLD badges, which are used to measure and distinguish mixed radiations such as β and γ radiations. Hence proper precautions must be taken while processing the radiation doses to the occupational workers and the public within the permissible levels. The staff assisting the patient, receives both direct dose from the patient and scatter dose from the walls, floor and ceiling (room components). The patient also receives this scattered dose. Hence, this paper presents and discusses the percentage of scatter dose, at various locations in a scanner room.   such dosimeters and also during dose estimation. However such alarming situations are less likely to exist, as the radiation worker is never exposed to the direct beam. Further it has been found that at surface, the D1/D3=2.0 for 6 MV photons whereas for 18 MV photons D1/D3=3.3 and is the artifact of the use of filters, used to distinguish and measure the radiation doses in mixed fields of beta and gamma radiation. However, with the increase in buildup thickness, the ratio of D1/D3 decreases. Various readout patterns and estimated doses for 6 and 18 MV photos are shown in Tables 1  and 2   energy fluence spectrum at various locations. 1 million photon histories were followed. Using energy fluence spectrum, air-kerma rates were estimated around the phantom and the statistical errors are within 2%. In order to study the influence of walls, floor and ceiling, the calculation were repeated without these components. Comparison of air kerma values at each detector location with and without the room components gives an estimate of scatter contribution from walls, floor and ceiling.

Results and Conclusion:
The percentage of room-scatter with respect to direct contribution from the patient is presented in the Table 1 for locations marked around the phantom as shown in Figure  1. The locations 1-6 are at 5 cm from the phantom. The Table  shows that the scattered air kerma rate around the patient is only coding is incorporated into the microcontroller using C-language. The leaf movement is controlled digitally by the H Bridge IC TPIC 0108B. The circuit is powered with 5 Volts for buffer, microcontrollers and feed back and 12 Volts to power up all the motors. The feedback of leaf position is obtained using the linear potentiometers which is coupled with the leaves. Using potential divider method, the change in resistance is converted into change in analog voltage which is calibrated for the linear movement of the leaf. i.e., 0.1V = 1 mm. Software is developed using Visual Basic language (VB) to read the treatment planning data in ASCII format and is stored in the MLC control computer. This enables to separate the useful data from the raw data and is displayed on the screen of the MLC control computer. When the program is executed, it sends the leaf position data to 0.6%. However, the dose to the patient is unaltered by the roomscattered photons. At 1 m depending upon the detector location the scatter varies from 9-16% of the direct air-kerma component from the patient. Near to walls the scatter contribution is almost 100% (see detector location 12 and 13). It is observed that the percentage room-scatter increases as the direct air-kerma rate component from the patient decreases due to dominance of the inverse square law. There may be an increase of scatter component as the area of the room decreases. From the results, it is seen that the technologist standing near the wall receives considerable amount of dose from scatter component scattered in comparison to the direct dose from patient. The study concludes that a PET room should have an adequate area to minimize the scatter to the staff involved. . m e d k n o w Multileaf collimators (MLC) are used to shape the beam for irregular shaped tumors which challenge the conventional techniques of radiotherapy and these are only available with linear accelerators. However the Isocentric Co 60 units are relatively inexpensive and found in most radiotherapy centers. Initially manual MLC was developed and later on it was motorized to accomplish the easy movement of the leaves. Now the motorized MLC is computerized in order to facilitate easy control of leaf movement. In this paper, the design and development of computer controlled MLC is discussed. Materials and Methods: MLC with 15 sets of leaves is developed using low melting alloy of height 9 cm with tongue and groove arrangement to reduce interleaf leakage. These leaves are made to slide in a carriage made up of duralumin and the leaves are coupled to 30 planetary geared Swiss motors through lead screws. The coupling is made with flexible joint to get smooth transmission and is made up of brass. This MLC is attached with collimator mount made up of duralumin and is fixed to the conventional collimator of the telecobalt machine. To enable the movement of MLC leaves, a control circuit is developed which is connected to serial port of a personal computer. It consists of a serial port buffer MAX232, 1 PIC 16F88 microcontroller, 3 PIC 16F777 microcontrollers and 30 H Bridge integrated circuits TPIC0108B. The serial port of the computer is used to communicate the leaf position data to the Microcontrollers. PIC 16F88 receives all the leaf data and transmits it to the PIC 16F777. Each PIC 16F777 Microcontroller controls 10 leaves. This the control circuit through serial port. The control circuit receives the data and calculates the error which is the difference of current position obtained from ADC and required position obtained from control software. The microcontroller nullifies the error by making the suitable adjustments in the leaf position for all leaves simultaneously.
Results: The performance such as field shaping, inter-leaf and intra-leaf transmission, dose delivery of Computerized MLC has been tested. The accuracy of leaf position corresponding to the field size is found to be ±1 mm. Conclusion: The motorized MLC has been successfully computerized for shaping Co 60 beam precisely. This could be used as a substitute for conventional blocks in static fields, there by eliminating the effort Introduction: Fluorescent X-rays provide a near monoenergetic  source of low energy photons, which can be used for the calibration of radiation monitors and detectors. Radiation measuring devices and instruments generally show a prominent energy response characteristics at low energy, hence it is important to measure their energy response in this region, specially for those detectors and radiation monitors which are specially designed to be used at low energy. Methods of generation of fluorescent X-rays has been given in the literature and experimental studies were carried out in the past. [1,2] Now a permanent set up has been made based on the earlier studies and various characteristic properties of these beams were measured to ascertain their suitability for the calibration work. This paper gives the methodology, details of the set up and the results of measurements.  Materials and Methods: Facility for the production of fluorescent X-rays has been established with the help of a dosimetry grade X-ray machine and three radiators viz. Cd, Mo and Sn. The potential of the X-ray machine is continuously variable from 15-320kV and the current is also adjustable from 0-30mA. Fluorescence X-rays are obtained by irradiating a radiator in the X-ray beam. The experimental set up is shown in the Figure 1. A 20 cm x 20 cm x 20 cm aluminium box having inner surfaces lined with 3 mm lead sheets has the arrangement to mount the radiators in the X-ray beams at an angle of 45°. The beam catcher is essentially a lead cylinder having 3 mm wall thickness used to minimise the contribution of scattered X-rays. Primary X-ray beam enters the box through a collimator assembly and the fluorescent X-rays are emitted in a direction perpendicular to it and pass through a collimating aperture. A 30 cc spherical reference ionisation chamber (A 4 , Exradin, USA) was used to measure the output of the fluorescent X-rays in term of K air and directional dose equivalent H' (0.07). The beam homogeneity factor was determined through measurement of first and second HVL. The first HVL was also used to evaluate the effective energy and the beam uniformity was ascertained with the help of radiographic film. Spectrum measurements were carried out using a spectrometer system with Cadmium Telluride detector. Results: Table 1 gives the measured value of various characteristic parameters of the fluorescent beams obtained with the three types of radiators. The Table also gives the typical measured value of K air and H' (0.07). The effective energy value measured by two other workers is also given for the comparison purpose. Beams were found to be uniform within 0.5% in a region of 5 cm radius around the central axis at 15 cm from the surface of the aluminium box. This ensures practically uniform radiation field over the dimensions of commonly used detectors.

Conclusion:
The results of measurements show that the fluorescent energy and the radiation field intensity for the calibration of radiation monitors and detectors in the low energy region.

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High energy radiation dosimetry using α α α α α-Al phosphor DR Mishra, MS Kulkarni, NS Rawat, KP Muthe*, SD Sharma**, SK Gupta*. Radiation Safety Systems Division, * Technical Physics and Prototype Engineering Division, ** Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai -400 085, India Introduction: Worldwide the conventional thermoluminescence (TL) approach towards radiation dosimetry is being gradually replaced by α-Al 2 O 3 :C based optically stimulated luminescence (OSL) dosimetry. [1] The OSL technique has found wide range of applications in the field of medical dosimetry for the in-vivo and in-situ dose measurements. We at BARC have recently developed an indigenous method for the synthesis of α-Al 2 O 3 :C phosphor [2] and related OSL readers for dose measurements for their applications in radiation dosimetry. The photon energy response (< 1.25 MeV) of this developed material is found to be linear up to 1Gy. The implications of these developments for high-energy medical dosimetry are discussed in the paper. Materials and Methods: The α-Al 2 synthesized using post growth Thermal Impurification Technique (PGTI) on crystalline Al 2 O 3 plates in reducing environment in presence of graphite. The α-Al 2 O 3 :C material so produced is found to have excellent OSL response in a wide dynamic range of 50 mGy to 1Gy for 60 Co irradiation. To find out the high energy O 3 :C OSL grade material is response of the α-Al 2 O 3 :C, the samples were optically bleached for 30 minutes under high intensity blue light (> 200 mW/cm 2 ), to erase the residual OSL signal, if any. The high energy photon irradiations (6 to 15 MV) were carried out on the α-Al 2 O 3 :C samples in full scatter condition, using tissue equivalent phantom, at a depth of 5 cm using three medical Linear Accelerators (Varian Clinac 2100C and Clinac 2100 CD and Siemens Primus) for an absorbed dose of 1 Gy. The samples were also irradiated to 1.25 MeV photons using 60 Co teletherapy machine (Theratron 780E) to an absorbed dose of 1Gy. The OSL measurements were done using photon-counting module in a programmable OSL reader interfaced to PC through an RS-232 serial interface. The samples were stimulated using continuous wave (CW) OSL mode with a 470 nm stimulation wavelength (∆λ≈20 nm, light intensity > 200 mW/cm 2 ). Result and Discussions: Relative response of α-Al 2 O 3 :C samples is shown in Table 1. Normalized OSL response of α-Al 2 O 3 :C for different

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±5 %) at the depth of 5 cm in the phantom. Since the size of the detectors is very small and the technique of OSL is dynamic, while making online in-situ measurements, α-Al 2 O 3 :C OSL phosphor could be used for in-phantom dose measurements in medical physics applications. 3 technique. Radiat Meas 2005;39:277-82. radiography which has been used for diagnostic imaging since 1983 and for portal imaging in radiotherapy with considerable success in recent times. Its digital nature gives several advantages over Commissioning of enhanced dynamic wedges using LDA-11 conventional films such as easier acquisition of images, economic R Suresh, K Ramalingam, G Arun, M Dinesh Kumar, M Babaiah. Yashoda running costs, filmless storage, quick transfer and multiple viewing Cancer Institute, Secunderabad, A.P, India of images using a Picture Archiving Communications System (PACS) network and easy analysis of images using suitable software. CR is Introduction: Enhanced Dynamic Wedge (EDW) an option in linear more versatile than Electronic Portal Imaging (EPI) in that the CR accelerators in which wedge shaped dose profile is created by the plate itself is physically film-like so that it can be placed inside a sweeping action of the Y-jaw from open to closed position while the phantom and irradiated from any direction. beam is ON. Varian Linacs implement dynamic wedges using Materials and Methods: Two MD40 CR cassettes (Agfa-Gevaert, Segmented Treatment Tables (STTs) which defines monitor units as Belgium) were used to acquire the images. Each cassette of size a function of the moving jaw position. For producing smaller wedge 14x17" (pixel matrix size, 2048 x 2494) consisted of a Ba.Fl.Br (Eu 2+ angles open field dose distribution are combined with a single 60 o doped) PSP plate. For this study, the dual energy (6 and 15MV) dynamic wedge STT known as EDW. Commissioning of EDW includes Primus and Mevatron linear accelerators (Siemens, Germany) and verifying the accuracy of both the isodose distributions and the monitor the Theratron 780C telecobalt machine were used. The cassettes units (MUs) generated by the treatment planning system. The dynamic were read-out using the CR reader, CR75 (Agfa-Gevaert, Belgium) nature of nonphysical wedges requires the use of a static linear array and the images in Digital Communication (DICOM) format were of detectors. The aim of our work is to commission the EDW configured transferred through an exclusive Radiotherapy PACS Network. Quality ECLIPSE planning system using LDA-11.
Assurance: Quality assurance tests were performed using the PSP Materials and Methods: Our institute is equipped with Varian Clinac plates to check the field congruence, field size and field shaping of DMX with millennium 26 pair DMLC and EDW in which the Y jaws Multi-leaf Collimators (MLC). Star shots were performed to measure moves to create dynamically wedge shaped dose distribution. The the isocentric shift for collimator, gantry and couch rotations. EDW profiles are measured in Scanditronix RFA-300 using Linear Dosimetry: The two PSP plates were individually calibrated at a Detector Array LDA-11 in dose integration mode. The LDA-11 has 11 source to detector distance of 150 cm. A water-filled penta stepdetectors spaced at 2.5 cm interval. When used in dose mode the phantom of perspex was fabricated for calibrating the PSP plates. electrometer integrates the dose for a complete EDW treatment for Absolute dosimetry was performed using a calibrated 0.14 cc ion fixed MUs. Then the detector is moved to a next position and the chamber (Capintec, USA). The calibration procedure involved: i) dose integration is repeated for same MU thus profiles were obtained Acquisition of CR images with step-phantom positioned isocentrically with 0.5 cm resolution. measured EDW beam profiles are compared with ECLIPSE TPS calculated dose profiles. For all wedges the effective wedge factors were measured for 6 MV photons for various symmetric field sizes using FC65G 0.6cc ionization chamber placed in SP100 water phantom at 10 cm depth with 100 cm SSD and compared with TPS values. For 10x10 cm 2 field percentage depth doses for a open field, 60 o EDW and physical 60º wedge were measured manually using parallel plate chamber in SP100 30x30x30 cm 3 water phantom and compared.
Results and Discussion: The EDW profiles measured using LDA 11 was compared with TPS calculated dose profiles. In high dose regions the dose differences was around ±3% and in penumbra regions the DTA was about 1 to 2 mm which might due to uncertainties in measurements. The measured effective EDW factors mostly agreed within 1 to 1.5% with TPS calculated wedge factors except for 45 o and 60 o wedges where for field size 20x20 cm 2 the factor varied by 2%. The EDWF decreases with increase in field size and wedge angle.
The PDD for open and EDW field were almost the same. The variation of depth dose measurements for EDW agreed within 1% with respect to depth and for physical wedge the PDD slightly increases with depth step-phantom positioned isocentrically and the polystyrene slab placed on the surface of the PSP plate. This was used to locate the positions of the ion chamber with respect to the step-phantom. iv) Plotting the calibration graph for pixel values (average value within the ROI of 8 mm x 10 mm) and dose. Dosimetric tests were done using PSP plates to find out the dependence on field size, energy and dose rate, percentage depth dose curves, beam profiles and inter-leaf and intra-leaf transmission for MLCs and Micro Multi-leaf Collimators (µMLC). MATLAB and imageJ were used to analyze the images.
Results and Discussion: The quality assurance tests mentioned were performed and the CR images obtained were analyzed. Compared to films i) it was much easier to acquire the CR images and ii) to accurately quantify the variations. The results were found to be comparable with those of films. The calibration graphs for each of the PSP plates were plotted relating pixel values and dose.
The results for the dosimetric tests were encouraging but not as satisfactory as for the QA tests. This was due the automatic post processing of the images done by the CR 75 reader and though this could be minimized it could not be completely turned off without disturbing the work flow of the Radiology department where the images were read out. Conclusion: Therefore it is concluded that CR using PSP plates is an excellent alternative for conventional films for quality assurance and a potential tool for dosimetry in radiotherapy.
Commissioning of enhance dynamic wedge in eclipse Introduction: Typically, a given telecobalt machine would have a set of wedges with different field size and different angle that would be attached to the telecobalt head. A number of developments in collimator head design has brought the concept Introduction: Enhance dynamic wedge (EDW) produce wedge of the ''universal and motorized wedge.'' Recently a new model of shape dose distribution by computer controlled movement of one the telecobalt unit, (Theratron Equinox-80, Theratronics, Canada) of the collimator jaws under simultaneous adjustment of dose rate.
with a 80-cm source to axis distance (SAD), has been first installed The relation between delivered dose and moving jaw position is at Tata Memorial Hospital in June 2007. This machine apart from defined by a reference table called "Golden segmented treatment the fully computer controlled operations employ the unique features table (GSTT)". Eclipse treatment planning system (TPS) uses pre-like asymmetric jaws (both X and Y), universal wedges (UW), a existing open beam data and GSTT to generate the Enhanced motorized wedge (MW) and a couch with the carbon fiber top. Dynamic Wedge fields. Our aim is to study the characteristic of The MW filter consists of a 60-degree wedge mounted in the EDW on the Linear accelerator (LA) and validate the absolute dose asymmetric collimator below the lead leaves and above the and profiles modeled by Eclipse TPS for EDW against measured tungsten trimmer bars. The leading edge of the wedge is positioned at 43 cm from the source surface. The lead leaves and the trimmer Materials and Methods: Effective wedge factor (EWF) bars move independently of the MW. The MW rotates together corresponding to EDW angles of 10, 15, 20, 25, 30, 45 and 60 with the collimator and is able to travel between two fixed positions: degree were measured as a function of field sizes ranging from in and out. Objective: Before clinical introduction of MW, it was to 20×20 cm 2 on Clinac 6-EX LA for 6 MV X-rays using a required to verify the performance of the treatment planning 0.13 cc ionization chamber positioned at 5 cm depth in a 35×35×30 process. In our department, the Eclipse, (Version 6.5) 3 dimensional treatment planning system (3DTPS) system (Varian, USA) was used for this purpose. The main objective of this paper was to report measurement at 10 cm depth. Off-axis profiles were measured both the methodology adopted to commission the motorized wedge in for physical and EDW having same standard wedge angles of 15, Eclipse. 30, 45 and 60 degrees using a 2D profiler kept at the isocenter of Materials and Methods: Dosimetric measurements in Equinoxthe machine. The accurate representation of EDW in Eclipse TPS 80. Measurements for motorized 60 degree wedge and universal was verified through absolute and relative dose measurement.
wedges (15, 30, 45 and 60 degrees) were carried out using a blue Eclipse TPS calculated MUs for 200 cGy at 5 cm depth were validated water phantom (Scanditronix Welhofer, Germany). Central axis for all available EDW angles using ionometric measurement on Clinac percentage depth doses (CAPDD) and off-axis cross-plane profiles 6-EX LA. TPS generated profiles across the wedge direction was were measured. For various filed sizes (2, 3, 4, 5, 6, 8, 10, 12, 15 validated by comparing with the measured profile on the treatment and 15x20 cm 2 ) for the motorized 60 degree wedge. The MW factor machine. TPS calculated EWF were compared with the corresponding was measured for various filed sizes (5, 10, 15 and 15x20 cm 2 ). A data measured on the linear accelerator. Results: For each EDW 0.6 CC cylindrical ionization chamber with and PTW Unidos angle, effective wedge factor (EWF) decreases with increase in field electrometer was used for this purpose. Commissioning and Quality size and found independent of the depth of measurement. The Assurance (QA) of MW in Eclipse: A hybrid generic water phantom decrease in EWF per cm 2 ranges from 0.0066 of 10 0 wedge to 0.0275 (30 x 30 x 30 cm 2 ) was used. Two beams of 10 x 10 cm 2 with a UW of 60 0 wedge. For 10 x 10 cm 2 field, the EWF measured at 5 and 10 and MW each were placed at source to surface distance (SSD) of cm depth agrees within ±1% for all wedge angles. EWF calculated 80 cm. A dose of 2 Gy was prescribed and normalized at the 10 using standard formula available in the literature agrees with the cm depth. The desired motorized wedge angle was obtained with data.
4×4 cm 2 cm 3 water phantom. Depth dependence of EWF was studied for 10×10 cm 2 field and for all EDW angles by repeating the measured value within ±1% for all wedges and up to 12x12 cm 2 field. This variation was found increasing up to ± 2% for field sizes up to 16x16 cm 2 . For field size larger than 16x16 cm 2 variation in EWF for 60 o wedge angle was 3%. Off-axis profile measured for EDW and physical wedges of same angle was found to be identical except in the penumbral region corresponding to Y-stop position. TPS calculated and measured EWF agrees within ±1% for all wedge angle and field sizes. The MUs generated by Eclipse TPS are also within ±1.5% of those calculated independently. Off-axis profile generated from the TPS for EDW and physical wedge of same angle was comparable. The mean variation between measured and TPS calculated dose at 5 cm depth with EDW of all available angle was found to be ± 3.0% (SD 3.5%).
Conclusion: EDW provides same dose profile as from physical wedge of identical angle. EDW have the advantages over the physical wedges because of technician convenience, option of multiple angles with 5° increment. The implementation of EDW in TPS provides an additional effective tool for conformal radiotherapy treatment planning. Furthermore, it improves efficiency by removing the need to mount and un-mount physical devices. Modeling of enhance optimizing the weight of the motorized beam. The calculated CAPDD and the dose profiles for motorized wedge beam were then compared with that of the UW beam for various field sizes and for standard wedge angles of 15, 30, 45 and 60 degrees. The dose was measured for a field size of 10 x 10 cm 2 only in a MEDTECH water phantom (30 x 30 x 30 cm 2 ) at 10 cm depth with a CC13 ion chamber (Scanditronix Wellhofer, Germany) and a NE electrometer (Nuclear Enterprises, UK). Results and Conclusion: The mean variation between measured and planned dose at 10 cm depth with MW was found to be 3.3% (SD 1.3). Figures 1 and 2 show the comparison of measured and calculated CAPDD and off-axis profiles for MW and UW respectively. The MW data for Equinox-80 was successfully commissioned in Eclipse TPS. It provides the capability of modifying the isodose characteristics of the radiation beam same as the UW. Thus MW can safely be used for clinical applications. Motorized wedges have the advantages over the standard (universal) wedges because of operator convenience. Further work, using chamber array, profiler, film dosimetry and TLD are planned to validate the present ionometric data.